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Geology Rocks Day 6: Gold in Them Thar Hills! + Geology Rocks Day 7: Fire and Faults

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Day 6 takes you down the Rogue and up Graves and Wolf Creek, through the heart of the Rogue River mining district.

Southwest Oregon was once home to hundreds of gold mines, which operated from the later 1800s to the 1940s. F.W. Libbey, an Oregon State geologist, wrote in 1963, “Gold mining was originally the mainstay of the economy of southern Oregon. It started settlements, built roads and schools, promoted local government, and established law and order. It is now at best only a token of its past.” Despite that fact that a lot of gold remains in the ground, mining today is still a shadow of what it was a hundred years ago. During World War II, gold mines were closed by government decree, because the labor and equipment was needed to mine materials critical to the war effort, which gold was not.  

There are two different types of gold mine in the area—lode and placer. In lode mines, gold occurs in narrow veins in the rock, typically mixed with quartz and sulfides, which are compounds of sulfur with metals like copper, lead, iron and zinc. Lode veins form when bodies of magma are injected into the crust of the earth and slowly cool. As the magma solidifies, chemical elements like sulfur, water, and metals are concentrated in fluids that percolate towards the surface through fractures in the rock. As the fluids cool, mineral crystals precipitate, filling the fractures with veins of ore. Mining lode gold is a difficult and dangerous process which involved excavating tunnels with dynamite to follow the veins.

Placer deposits on the other hand are much easier to mine. Placer gold forms when the rocks that encase ore veins are weathered and eroded away over millions of years.  Gold is essentially indestructible at the surface of the earth, so that long after the mountain that held the vein has crumbled into sand and been washed to the sea, the gold contained in the veins is still fresh, and gets trapped in the sediment at the bottom of streams and rivers. Gold is one of the densest elements known, twice as dense as lead, so even very fine particles are hard for a river to move, and they accumulate in river gravel. There is still placer gold in most of the rivers of southern Oregon, including the Rogue, but most of the richest placer mines were in river terraces, like the ones you rode across on Day 5.

Lode gold mines are common in the hills surrounding Galice and Indian Mary Park, and you will see an obvious example at mile eight, just past the Almeda Park. You will pass a big road cut on the right made up of crumbly yellow-orange and red-stained rock. This is a zone of mineralized rock that hosts the ore veins that the Almeda mine followed, with thousands of feet of underground tunnels and shafts that have long since been closed or collapsed. The mine produced gold, silver, copper, and lead for many years in the 1930s and 1940s. As you ride down the Rogue and then turn up Graves Creek, you will be passing numerous old placer

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Old placer mines along Graves Creek show as ragged pits on the smooth surfaces of old river terraces in this perspective view of lidar imagery.

mines on the ancient river terraces that now lie high above the modern streams. Mines with names like the Lucky Shot, Golden Light, and Vindicator recall a time when mining was the mainstay of the local economy. Using recent lidar topographic scanning data, we can see the scars left by large-scale placer mining in the days before reclamation of mined lands was required. These older mines were typically worked using hydraulic mining. Hydraulic mining relied on a network of ditches to bring water to the mine from surrounding creeks, and the water was then sprayed at high pressure through a giant iron nozzle, called a monitor. The resulting stream tore away the loose gravel holding the gold and sluiced the material into boxes designed to trap the gold and pass the remaining sediment out. This was a very cheap and effective form of mining, but left damaging amounts of sediment in streams and rivers, and it is no longer allowed.

After you leave Wolf Creek and begin the climb along I-5, you will have plenty of time to admire a huge road cut along the interstate. The road cut is composed of a rock geologists call greenstone, largely because it is green. Greenstone is a catch-all term for a wide range of metamorphosed volcanic rocks, which typically are green because they contain two iron-rich metamorphic minerals, chlorite and epidote. Iron is one of the most common sources of strong colors in rock, producing yellow-orange and red when it is in the oxidized form, and green when it is reduced. You will see more road cuts of greenstone along the road to the lunch stop and the return to Glendale.

 

Geology Rocks Day 7: Fire and Faults

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The ride down Cow Creek will take you through the heart of the 2013 Douglas Complex fire. Areas shown in red were severely burned. Orange means moderately burned, and green lightly burned. You will cross the Canyonville Fault and pass beneath Nickel Mountain, site of the only nickel mine in the US.

The final day of riding takes you down the valley of the beautiful Cow Creek. For much of the day, the geology will be the familiar rocks of the exotic terranes, mélange, greenstone, and serpentinite.

From 6 to 10 miles into the ride, you will enter a long stretch that was severely burned in 2013 by the Douglas Complex Fire. This fire, which was started by lightning, covered over 44,000 acres and was controlled thorough the efforts of over 3,000 firefighters. The fire may have cleared away enough vegetation that you will be able to see some old placer mines on both sides of the road at about mile 8. These mines, on high river terraces, produced gold and in some cases platinum and chromite. Platinum and chromite are minerals that are found in ultramafic rocks, so it is no surprise to find them in placer deposits where the bedrock includes serpentinite. You will see the Douglas Complex fire again from miles 12 to 20.

At mile 25, you will cross a major fault, called the Canyonville Fault, which extends for 50 miles east to west through the area. When you cross the fault, you will once again see the thick sedimentary turbidite layers that you saw in the Tyee country on Day 2. But the fault is actually very complex, so you will pass through alternating slivers of exotic terranes, and thick beds of turbidite sandstone and conglomerate. You will see a great outcrop of tilted turbidite layers at about mile 32, just before you come out into the wide valley at Riddle.

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In this perspective view derived from lidar imagery, tilted sandstone and conglomerate layers are clearly visible from the road near mile 32.

Shortly before you turn off Cow Creek Road onto Glenbrook Loop Road, you will see what appears to be a large industrial facility to the left, with big piles of crushed rock, and you may notice a large bare patch at the top of the mountain behind the stockpiles.  This is the remnant of the Hanna Nickel mine, which is the only significant nickel mine to have operated in the US. Despite having relatively low grade ore, the mine was opened with a US government subsidy because of concern over dependence on foreign sources of nickel, a strategic metal. When subsidies were halted in the 1980s, the smelter continued to produce nickel form higher grade imported ore, but it was ultimately closed and sold for scrap.

Ian Madin is the Chief Scientist for the Oregon Department of Geology and Mineral Industries and in his spare time provides geology blogs for the Cycle Oregon. He will be providing commentary during the evening program and will be a available to answer questions during the ride.

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Policymakers Ride: Advancing Important Projects in Washington County

On Friday August 19, more than 100 elected officials and civic leaders rode the 12th annual Policymakers Ride in Oregon’s Washington County. Since the ride began in 2005, Cycle Oregon has helped stage this annual event that initiates discussion about regional challenges related to water, population, tourism, and transportation management systems.

This year’s 27-mile ride—which went from the Fernhill Wetlands in Forest Grove to Greenville City Park in Banks, and back—focused on the Portland metropolitan area’s “West Side Story,” a rapidly growing network of cycling and walking trails.

28479262493_fc090dcfc4_zMembers and allies of the Intertwine Alliance started the day with a tour of the nationally recognized Fernhill Wetlands wastewater management facility. Riders departed Fernhill with a belly full of scones, burritos, quiches, and cinnamon rolls from Maggie’s Buns in Forest Grove. They rode past farm fields to the village of Verboort, famous for its towering sequoia groves and annual handmade-sausage festival.

Under the welcome shade of the sequoia trees, riders learned about the intersections of agriculture and water management, which has helped grow the nursery business in 29020559171_8cf0972162_zWashington County. Riders headed north toward Banks, where they took the Banks-Vernonia trail to a stop at the Vandehay Ranch. There, riders heard about Metro’s upcoming levy to secure open spaces and fund conservation efforts, and about Oregon State Parks Scenic Bikeway program.

Riders found shade back at Greenville City Park in Banks, where lunch by the Trailhead Café was served. They heard about the growing tourism economy in Washington County, including award-winning wines and world-class bicycle routes—the Yamhelas Westsider Trail, a scenic trail through wine country, is on the list for future ride routes. Riders also heard about the latest news on the Salmonberry Trail, which holds the promise of connecting Portland with the coast along a historic 84-mile route through the Tillamook 28811171360_989678d0ee_zState Forest and many chapters of Oregon’s history.

The return to Fernhill was hot, but conversations about advancing many important projects helped the miles pass quickly. Temperatures were flirting with 100 degrees by the time the peloton crossed the finish line, where riders were greeted in true Cycle Oregon fashion by an ice cream truck!

Photos by Scott Mizée and Jonathan Nicholas. Special thanks to our partners and sponsors of the Policymakers Ride.

PMR Sponsors

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How to Have Fun and Stay Safe on an Organized Bike Ride

il_fullxfull.384476172_tm43Organized rides across the country are getting pushback from communities that are frustrated by riders who flaunt the rules of the road. Besides crashes and fights, some communities have disqualified permits, and insurance companies have denied event coverage. If you’re participating in Cycle Oregon’s Week Ride this month, or really any ride, please be courteous and—above all, be safe.

If you’re gearing up for the Week Ride, you’re about to embark on an epic adventure, one that has the ability to change lives in a positive way. You’re helping raise money for some great causes. You’re getting the chance to meet some amazing people from some of the most awesome communities in the world. And last but not least, you get to spend an entire week with over 2,000 people who have at least one shared passion.

You might not know a lot of your fellow riders today, but that’s about to change. Soon, you’ll be friends who feel like family. One of the very best ways to allow this camaraderie to blossom is to do your part to make sure that everyone is having as much fun as you are. Here’s how:

Glee-CO14 (290)Maintain road awareness
You’ll be on some pretty rural roads most of the time, but there will always be traffic. You, your fellow riders, Cycle Oregon support vehicles, motorists, and people who live in the area are all going to be sharing the road. Knowing at all times what and who is around you is a great help to you and everyone else. Keep your eyes and ears open, and frequently check your six.

Consider a mirror
From Bike Gallery’s Aaron “Rambo” Harrison: Bicycle mirrors help create awareness of what’s behind you while riding, helping you ride more predictably and safely. Mirrors come in three basic flavors: handlebar-mounted, helmet-mounted, and eyeglass-mounted

Handlebar-mounted mirrors have long been a popular option, especially if you just want a basic idea of what’s going on behind you. Unfortunately, the advent of integrated brake/shift levers have forced handlebar mirrors for road bikes to move from the brake-hood down to the end of the handlebar. While there are some excellent fish-eye mirrors, which provide a fairly large field of view, they’re very affected by the vibration of the bicycle (and the distortion created by the lens’s shape).

Helmet mirrors have become the most popular option among cyclists riding road bikes or recumbents. They are much less affected by road vibration, and since they sit much closer to your eye, they provide a significantly larger field of view.

Eyeglass-mounted mirrors are much like helmet-mounted mirrors, but they mount on one of the temples of your glasses instead of your helmet. Many modern sports glasses don’t have flat enough surfaces to mount them. If you wear prescription eyewear with straight temples, these are a good option.

JEK_5432-SPosition yourself strategically
If you’re a slower rider, keep to the right. If you’re a faster rider, give those you pass a wide berth. If you’re being passed, move to the right. If you’re going to stop, move over to the right before doing so—especially if you’re on a steep climb. If that’s not possible, make sure no one is right behind you before you jump off. If you have no reason to change your position, hold your line.

 

Communicate
If you notice a car coming from behind, let your fellow riders know by calling “car back.” If you see a car coming toward you, it’s “car up.” If you’re passing or stopping, let that be known as well. Likewise, if you notice a hazard, point it out. If you want to give a hand signal, point toward the hazard, not in the direction someone needs to go to avoid it.

Pass properly
Before you pass, check behind you and to your left before you make your move. Assume another rider or a support vehicle is passing you at all times. This is something a lot of folks tend to forget. Keep in mind that support vehicles are often driving slowly and quietly until it’s safe to pass riders. Don’t assume you’ll hear them.

If there’s a car behind you or someone is passing you, hang back a few seconds until the coast is clear. Also, when you hear “car back,” wait to initiate your pass until the car goes by. Going for the quick pass when you hear “car back” is dangerous and obnoxious. When you finish your pass, move back to the right when it’s safe to do so (someone might want to pass you, Speed Racer). Don’t pass someone who is in the process of passing someone else.

Remember, this isn’t a race, and your desire to get around slower riders should never put you or them in jeopardy. We never run out of beer, food, or places to pitch your tent.

Glee-CO14 (55)Obey traffic laws
All of them. It’s amazing how many people do blatantly silly stuff. Blowing off a stop sign isn’t a good idea. Blowing off a stop sign WITHOUT EVEN LOOKING FOR TRAFFIC is just dumb. And it’s something we see frequently. If you’re going to stop along the route, Oregon law dictates that you pull off the road. It also requires riding single-file if there’s traffic behind you. Keep in mind that the motorcycle police who accompany us can and will issue tickets as warranted.

Paceline politely
Riding in a paceline is a lot of fun, particularly if you’re a skilled and seasoned rider. (It is never recommended to paceline with people you are not used to pacelining with.) But your fun should not come at the expense of everyone else’s fun—not to mention safety. Please restrict paceline riding to areas where it’s safe. If your whole group can’t safely pass riders, don’t pass. And if you have to drop off your paceline to avoid putting someone else in danger, do it.

Share the road
“Share the road” is not simply a saying to remind motorists that they need to make room for cyclists. It works the other way around, too. On an event like Cycle Oregon, it’s important to leave room for traffic. Riding three (or four or five) abreast while letting cars stack up behind you is not sharing the road. Moreover, it isn’t the way to endear ourselves to the local motorists, many of whom are our hosts. We’re ambassadors of our sport, and the way we conduct ourselves on the road matters.

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Geology Rocks Day 5: Serpentine Rocks and Roads

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Day 5 route: You’ll follow the Rogue River until you reach Agness, then climb over Bear Camp Road, which snakes its way between the Wild Rogue Canyon and the Kalmiopsis Wilderness.

The route on Day 5 takes you up the Rogue River to the confluence with the Illinois River near Agness before turning off and climbing the Bear Camp Road to get around the road-less Wild and Scenic canyon of the Rogue River. You will see a wide range of rocks today, along with some wild and beautiful scenery, and end up in the heart of Oregon’s gold country. Gold Beach is so-named because a century ago, gold was being mined from the beach there.

As you leave Gold Beach, you will pass the HWY 101 bridge you came in on, and turn inland. A quarter mile past the bridge, you will pass a spectacular road cut made of serpentine. You will have seen serpentine several times before, but this is a particularly nice example—sea-green to deep blue and shiny.

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Serpentine is a rock made of the mineral serpentinite, and it is a clue that you are looking at rocks that have been very deep in the earth. Serpentine is formed when ultramafic rocks come close to the surface and begin to react with water. Ultramafic rocks (meaning that they contain a lot of magnesium and iron) are part of the earth’s mantle, the rocky body of the earth, which typically begins between 5 and 20 miles beneath the surface. Subduction actually involves jamming big pieces of the earth’s crust into the upper part of its mantle, so it is not surprising that pieces of the mantle get shoved to the surface in the process. These mantle rocks are made of minerals that formed under great pressure and temperature, and when exposed to water as they near the surface, they react to form serpentinite. Serpentinite is soft and weak, and much less dense than the minerals it came from. This means that as it forms, it expands, and actually begins to rise.

Personal experience tells us that rocks are hard and rigid, so it is difficult to visualize how rocks might bend and flow like putty or liquid, but over long periods of time, they do! This means that if there is a body of rock of low density in the earth’s crust, it will rise through the crust, just as a hot air balloon rises through the atmosphere. Soft, low-density serpentine tends to rise through the crust, typically along fault lines. This means that by the time it gets to the surface, it has been repeatedly kneaded, and it is shot through with slip-planes that have been polished to a mirror finish. This is why it appears so shiny.

Of course, it also makes for weak slopes. Shortly after the big serpentine outcrop, you will be riding across large landslides, until you get to Saunder’s Creek (~ mile 3), where you will ride onto river terraces and find some of the most level riding of the day. River terraces form much like the coastal terraces of Day 3. During periods of stable climate and sea level, rivers tend to widen their valleys by eroding from side to side, leaving a layer of sediment across the valley floor. When there is a climate shift or ice age, the river will begin to erode downwards, cutting into the old valley floor and eventually leaving it high and dry, preserving its sediment layer. As with coastal terraces, there are often several levels preserved along a river valley.

Just before you reach the Illinois River, you will cross out of the mélange and serpentinite and landslides, and once again be riding thorough the turbidite sedimentary layers that you saw on Days 1 and 2. You will see distinct layers in the mudstone and sandstone in many of the road cuts as you turn away from the Rogue and start to climb Bear Camp Road.

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Bear Camp Road is a BLM access road that is the shortest route between Grants Pass and the coast in summer, but it’s closed with snow in winter. Tragically, a family was trapped in the snow on this road several years ago when their GPS system directed them over Bear Camp in the winter. After several days, the father left the car to try to get help, descended a steep canyon into the road-less stretch of the river, and died of exposure. The family was subsequently rescued through analysis of weak cellphone pings.

The twisty course up Bear Camp road will include patches of gravel road, the result of constant small landslides that occur in the weak shale and mudstone layers that make up much of the climb. You will pass back into exotic terranes and mélange shortly before lunch. After lunch, you begin a protracted descent, a “serpentine path,” as you wind your way down through the rugged terrain carved in the mélange. You will see a wide range of rocks in the road cuts, with many different colors and textures. Many have been so changed by the heat, pressure, and violence of the subduction process that they are very difficult for a geologist to identify. The last few miles of your descent are along Galice Creek, which was the heart of the local mining district, and which you will see more of on Day 6.

Ian Madin is the Chief Scientist for the Oregon Department of Geology and Mineral Industries and in his spare time provides geology blogs for the Cycle Oregon. He will be providing commentary during the evening program and will be a available to answer questions during the ride.

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Geology Rocks Day 4: Beauty and the Beast, On the Trail of The Big One

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Figure 1. Overview of the Day 4 route. Red areas are landslides recently mapped using lidar, a high-accuracy-laser scanning technique.

The layover day ride down Highway 101 to Brookings is one of the most beautiful stretches of coast in the world. You should try to ride at least a part of it. Steep rugged mountains drop into the sea, and clean empty beaches are interspersed with thick forest, sheer cliffs, sea stacks, and arches. For those in need of a rest before the Day 5 climb, a jet-boat ride up the Rogue River, one of the premier fishing and whitewater rivers in the west, is almost as beautiful.

The rocks continue to be a variety of exotic terranes, made largely of mélange, folded and broken sandstone, and serpentine. You will see patches of bright green serpentine just south of Gold Beach after you cross Hunter Creek, just south of Cape Sebastian, and between Myers Creek and Pistol River. In many places you may see large knockers standing out on the open grassy slopes. The highly varied geology of mélange and knockers is largely responsible for the spectacular coastal scenery, as the waves accentuate the chaotic nature of the bedrock to produce a dramatic coastline.

You may have a harder time noticing that the slopes above, and sometimes beneath, the highway are riddled with hundreds of landslides. Using new laser-scanned topographic maps, geologists have identified several thousand ancient landslides lurking along the slopes of the coastal mountains between Gold Beach and Brookings, making this area one of the most landslide-rich in the country.

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Figure 2. The broken rocks of the exotic terranes make for spectacular coastal scenery with many cliffs and offshore rocks and islands. The orange line marks the route.

The force behind this landscape, both the 200 million-year-old mélange and the very recent landslides, is subduction. Subduction happens where an oceanic plate and continental plate collide, and the oceanic plate slides slowly beneath the edge of the continent. The boundary between the plates is a fault zone, typically hundreds of miles long, along which the ocean plate drives beneath the continent in a series of 50-foot jerks, separated by hundreds of years of steady buildup of pressure.

These jerks are called subduction megathrust earthquakes, and are typically magnitude 8 to 9. The magnitude-9 earthquake in Tohoku, Japan in 2011 is the most memorable recent example. During each earthquake, the rocks along the fault get broken and mixed, and over millions of years, after thousands of earthquakes, a thick layer of broken rock forms around the fault. This is how the mélange we see in the hills is formed, and in the case of these exotic terranes, the earthquakes that formed them occurred hundreds of millions of years ago, along a subduction zone that died 150 million years ago.

However, a new subduction zone started up along the Pacific Northwest coast perhaps 50 million years ago. It is still active, and is slowly building up stress today, preparing for the next megathrust earthquake. In between earthquakes, the fault is locked and both plates move together. In fact, an ultra-precise GPS station at Cape Blanco, our Day 3 option destination, is currently moving towards Alberta, Canada at the rate of a little over a half inch a year. At that rate it has moved, along with all of western Oregon and Washington, about 15 feet since the last Cascadia megathrust earthquake in 1700 AD. At the scale of tectonic plates, the crust of the earth is flexible, and it can bend like a bow as shown in Figure 3. As the oceanic plate pushes against the continent along the locked fault, the rocks along the coast not only move steadily to the NE, they also rise as the continent flexes under the strain. When the earthquake finally occurs, the flex relaxes and the whole edge of the continent lurches 15-30 ft back towards the southwest, and the rising areas along the coast subside as the flex relaxes. Fifty miles offshore, the leading edge of the continent rises abruptly, displacing a huge amount of water and producing a bulge on the surface of the ocean. As the bulge of water collapses, it sends out huge tsunami waves, which arrive on the coast in as little as 15 minutes.

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Figure 3. The subduction earthquake cycle. The colliding plates remain locked for centuries, slowly bending as stress builds up. When the earthquake occurs, the bent plate snaps back, and the tip of the overriding plate flips up, making a huge bulge in the ocean surface, which turns into a devastating tsunami.

Computer models of potential future waves have been completed for the entire Oregon coast, and in many parts of coast you are riding today, waves as high as 80 to 100 feet above sea level are possible. The tsunami in Japan in 2011 killed over 16,000 people who were unable to evacuate in time, so it is important to know how to evacuate safely in the unlikely event of a Cascadia tsunami. You can download an app for your phone to show the way to safety or view evacuation maps for Oregon coastal communities here.

quake

An incredible job of geologic sleuthing has shown that the Cascadia subduction zone has produced 42 megathrust earthquakes in the last 10,000 years, 19 of which were magnitude 9 to 9.2, and another 23 of “only” magnitude 8 to 8.7. The thousands of landslides along the coast are largely the result of this violent history.

In addition to generating a tsunami, the next Cascadia earthquake will cause very strong shaking along the coast for up to five minutes, which in turn will trigger landslides to move on the steep coastal slopes made up of sheared and shattered mélange rock. Geologists expect to see thousands of landslides occur during the next Cascade earthquake, and Highway 101 may be blocked for years.

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Figure 4. Looking east at the coast and ocean floor, you can see where the route lies in relation to the Cascade Subduction Zone. The giant fault slopes back beneath the land, and the red line on the ocean floor marks the point where it reaches the surface of the earth. This red line corresponds to the purple line on the first panel of Figure 2.

The giant fault that produced all of these earthquakes lies just a few miles off the coast along the ride, and because the fault slopes gently to the east underground, it is only 15 miles away from the route, straight down. Don’t worry: The odds of an earthquake occurring on the day you ride the coast are about 1 in 50,000! This Pulitzer-prize-winning article about the impact of the next Cascadia earthquake is worth a read.

Ian Madin is the Chief Scientist for the Oregon Department of Geology and Mineral Industries and in his spare time provides geology blogs for the Cycle Oregon. He will be providing commentary during the evening program and will be a available to answer questions during the ride.

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