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Geology Rocks – 2018 Classic

Ian Madin has worked as a geologist with the Oregon Department of Geology and Mineral Industries for nearly 30 years. In his spare time he enjoys riding with Cycle Oregon and sharing stories about the incredibly cool geology of Oregon.Figure 1. Features of the 2018 route. We will see three mountain ranges (Elkhorn, Wallowa and Blue), four valleys (Baker, Eagle, Pine and Grand Ronde) two great plateaus (Palouse and Joseph) and one great hole in the ground (Hells Canyon).


The 2018 Classic ride takes us on a grand loop around the mountains of northeast Oregon, a region of incredible contrasts. We will see rich agricultural valleys, lonely sagebrush steppes, dense old growth forests, jagged mountains, an enormous gorge and rolling wheatlands. Although the terrain and vegetation are diverse, the geology is fairly simple with three major types of rock along the route. Underneath it all lie exotic terranes, remnants of ancient seafloor that have been crumpled and cooked as they were plastered onto the edge of North America by plate tectonics 150 million years ago. The exotic terranes are covered by the Columbia River Basalt, a thousand or more feet of black lava layers that buried the entire landscape 16 million years ago. Sand, gravel and clay layers deposited by lakes and rivers over the last few million years cover the older rocks in most of the valleys. The spectacular landscape of our ride is the result of powerful forces that have faulted, folded and eroded this relatively simple geology into rugged ranges, deep valleys, broad plateaus and one giant hole in the ground.

 Day 1: Baker City to Halfway

On Day 1 our ride will cross areas of dark broken rock of the exotic terranes and light colored sand and clay layers of the ancient lake beds as we descend into Eagle Valley. Leaving Richland we will climb over a high ridge of Columbia River Basalt, before descending across a large active fault line into the Pine Valley and our camp in Halfway. Eight miles into the ride, we will pass the Oregon Trail interpretive center, and for the next few miles you will see many roads and areas of excavation to your right. This is the Virtue Flat gold mining district which had a rich history of underground mining from the late 1800s to the mid 1900s. 31 miles in we will pass the Hole in the Wall landslide, which briefly dammed the Powder River when it let loose in 1984.

Day 2: Halfway to Wallowa Lake

Day 2 starts with a ride across the Pine Valley, where sediment from the Wallowas fills the hole formed as the valley floor subsides along the big fault we crossed on Day 1. Leaving the valley, we will ride through Columbia River Basalt layers for most of the rest of the way. Don’t miss the McGraw overlook into Hells Canyon, where you will see bold layers of basalt flows making up the upper slopes, and smoother lower slopes of the exotic terrain rocks. The Snake River that you can see from the overlook is 3,850 feet below you. We will cross the Imnaha River canyon and several smaller canyons before emerging at the south end of the Joseph plateau, which extends north for 50 miles. On our left, the steep front of the Wallowas rises 5,000 feet above the plateau, the result of millions of years of steady movement along a great fault at the foot of the mountains. Our last few miles to camp will be along the shores of Wallowa lake, which is hemmed in by glacial moraines; great piles of rock rubble brought left by the glacier that once filled the lake basin.


Day 3. Wallowa Lake to Elgin

Leaving  Wallowa Lake and Joseph we will ride down the Wallowa River with the steep eastern front of the Wallowa Mountains on our left and a broad grass-covered plateau to our right.  The rocks beneath our feet consist of Columbia River Basalt layers a thousand feet thick, and the layer at the bottom of that pile matches a layer on the summit of the Wallowas above Joseph.  Thousands of large earthquakes have occurred here over the last million years, each lifting the mountains up a few more feet, until the basalt layers have been separated by over 6,000 feet. After we pass the confluence with the Minam River, we start to climb out of the canyon along a long road cut that exposes several layers of Columbia River Basalt,  You will be moving slow enough to appreciate the hexagonal cooling columns and bright red layers of baked clay between lava flows. The last bit of our descent into Elgin crosses a big landslide, one of many in this area that occur when the clay beds between the basalt layers get wet and become geologic grease. Just north of Elgin you can see Jones Butte, a small forested volcanic cone.  At 2 million years old, it is by far the youngest volcano in the area.

Day 4. Elgin to Pendleton

Leaving Elgin we cross a large fault just as we pass the log yard at the mill. If you look to the right, you can see the steep straight mountain front formed by the fault; a smaller version of the front of the Wallowas. Across the fault we climb to the crest of the Blue Mountains, and also climb steadily higher in the stack of Columbia River Basalt layers.  These layers have distinctive characteristics that allow geologists to identify them throughout Oregon, Idaho and Washington. Their names evoke the geography of the region: Grande Ronde, Lookinglass, Wanapum, Ginkgo, Umatilla, Rosalia, Umtanum and my personal favorite, Fiddler’s Hell. Once we start our descent, the transition from the forested slopes of the Blue mountains to the endless rolling plains of the Palouse is one of the most amazing views in Oregon.  The Palouse is a broad plateau built on horizontal layers of Columbia River basalt up to two miles thick. It is covered with windblown silt called loess, which makes for rich agricultural soils. The loess was brought into the area during the last ice age, as the continental ice sheet ground rock to flour, and meltwaters flushed the rock flour down the Columbia River where the winds picked it up.

Days 5, 6 and 7

Day 5. Pendleton to Echo to Pendleton

The loop across the Palouse to Echo and back along the Umatilla River is a beautiful ride. Leaving Pendleton we climb onto the rolling loess (windblown glacial silt) plain, crossing many miles of dryland wheat fields, which soon give way to green circles of irrigated alfalfa and other crops. Where the road starts to take a series of right-angle bends, we enter into an area that was swept by the great ice age floods. During the end of the last ice age, huge lakes formed in Montana where the ice sheet blocked valleys. The lakes would fill until the ice dam floated, releasing unbelievable quantities of water that roared across eastern Washington on their way down the Columbia. This happened dozens of times, leaving large areas scoured deeply into bedrock, and other areas covered in gravel, sand and silt carried by the raging waters. At Echo, the flood waters were nearly 200 feet deep, and probably moving faster than most of us can ride! We return along the Umatilla River through a small canyon carved though layers of the Columbia River basalt, and the route mixes rolling grass and sagebrush covered hills, red, black and brown basalt cliffs, and lush riverside vegetation. You will see more of the typical basalt columns layered with areas of broken and porous basalt.

Day 6. Pendleton to La Grande

Leaving Pendleton we climb the old route up Cabbage Hill, where large faults have lifted the Blue Mountains above the Palouse lowlands. Columbia River Basalt flows in Pendleton can be matched with identical flows at the crest of our ride, thousands of feet higher. We wind across the top of the Blue Mountains until we begin our descent into the Grand Ronde River canyon, slicing deep into the layers of basalt, and crossing dozens of faults. In the Canyon, keep an eye out for patches of bright white soil along the banks of the river. These are deposits of Mazama ash, which was blown into the stratosphere by the eruption that formed Crater Lake, 250 miles away. There are many interesting features in the Grande Ronde Canyon, including dozens of small faults, large landslides, and at Perry, an abandoned meander. This is an area where the Grand Ronde River carved a horseshoe-shaped bend through the basalt, which got tighter and tighter until it was cut off and left high and dry. We leave the freeway just as we cross the West Grande Ronde Valley fault, which has lifted Mt. Emily (the high point visible north of town) more than 4000 feet above the valley floor.

3D lidar view of the Grande Ronde Canyon at Perry, showing large landslides and an abandoned meander of the Grande Ronde River.

Day 7. La Grande to Baker City

We start across the flat floor of the Grande Ronde Graben and pass Hot lake on our way to the town of Union. Hot Lake is a high-volume hot spring, where water at 180 to 200 F (82-93 C) gushes up along a fault line that runs along the base of the mountain. Hot springs either form around young volcanos, where there is hot magma near enough to the surface to heat ground water, or in areas where large faults allow cold ground water to circulate deep in the earth where it is heated and then rises back to the surface. Hot Lake was developed as a grand resort and sanatorium in the 1920’s and 1930, but fell into disrepair over the years. The resort has been restored to much of its original glory over the last decade by the Manuel family. There is another hot springs at the town of Cove, a few miles east of Union, and we will pass a few miles from Radium Hot Springs in the town of Haines as we ride through the Baker Valley. All of these springs form where faults allow groundwater to circulate deep into the earth where temperatures are naturally high. One local water well was drilled to a depth of 3000 feet, and produced water at 110 degrees!

We climb a low pass out of the Grande Ronde Valley at Union, and enter the Baker Valley at North Powder.   We finish our ride across the Baker Valley with the Elkhorn Range dominating the skyline to our right. The Elkhorn Range is a block of the ancient exotic terrane rock that has been uplifted by recent faulting, much like the Wallowas, Blue Mountains and Mt. Emily in the Grande Ronde Valley.

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