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About the Route – Classic XXXII Day 2

The day starts out with an Ansel Adams-worthy-view of cliffs framing the John Day River as it meanders through green farmland – and it only gets better from there. The landscapes we ride through today are as varied as they are jaw-dropping. Great spires of rock complete with soaring raptors gradually transition to ancient cliffs that closely resemble melted candles. There have been forces at work here for millions of years diligently crafting and coloring everything in sight, making this journey through time one you could only ever experience right here.

Main Route: 59.6 miles / 3,226’ elevation

Roll out of Monument and head east for a long section of flatish miles but take it easy and save something for the final push up and over to Fossil. From the start at around 2,000’ above sea level riders bump up right away to a little over 2,100’ but then gradually drop over 40 miles to 1,650’ . From the rest stop at Service Creek the route turns northwest and finally tilts upward at a continuous, but moderate, incline for ten miles until Butte Creek Summit at 3,791’. From here it’s time to enjoy the gravity assist for another ten miles and power on into Fossil sitting at 2,654’. 

Riders cross over from Grant County to the aptly named Wheeler County as they approach Kimberly, Oregon, named for the Kimberly family who established commercial orchards here in the 1930’s. The route follows the John Day River to a rest stop in Spray, Oregon, the former location of a ferry that was an important regional crossing of the river. Camp for the evening is the county seat for Wheeler County and home to Oregon’s only legally accessible fossil digging site, the Wheeler High School Fossil Beds, which are a short walk from camp. These fossil beds represent the bed of a shallow lake that existed here about 33 million years ago, during a time period known as the Oligocene. Plant fossils found here include the ancestors of modern sycamore, maples, oaks, rose, and alder and while no large animal fossils have been found some aquatic vertebrates, including a salamander and small fish are included here.

Long Route: 68.6 miles / 5,094’ elevation

Riders wishing to add even more climbing to the day’s route can add the climb north out of Spray up Winlock Road. About a third of the way up the climb riders will pass by Corncob Creek and the historic Corncob Ranch. In the early 1860’s a group of U.S. soldiers were hiking in the area and discovered piles of corncobs in the area of a Native American summer encampment and gave the stream its name. The historic ranch, centrally located to all four of the Fossil Bed sites, is now available for camping and RV stays. Visit Travel Oregon’s site to learn more. The climb tops out just over 3,200′ and descends gradually back to the Main Route along the John Day Hwy just a few miles before the Service Creek rest stop.


Geology Rocks! by Ian Madin

Ian Madin worked as a geologist with the Oregon Department of Geology and Mineral Industries for 32 years and has ridden with Cycle Oregon for over a decade now. Here, he gives us a look at the the cool and sometimes hidden geology of the regions through which we ride. His nightly presentations at Classic are always fun and informative so grab a cold beverage or dessert (maybe both!) and grab a seat when we get him on the mic.

Be sure to read Ian’s Classic XXXII Geology Rocks! preview feature first. You can find it on our blog here.

About the Route Classic XXXII Day 1 is here.

View all Classic XXXII routes on Ride with GPS here


The undulating unconformity – Leaving Monument, the route immediately encounters a dike of Columbia River Basalt (CRB).  A dike is a body of rock formed when molten magma is injected into a crack in existing rocks.  In many cases the dike will feed an eruption at the surface, but when the eruption ceases, the molten rock cools to form a vertical sheet of basalt that cuts through the surrounding rock.  Here the dike is cutting through white and pink ash of the John Day Formation, and you can see the edge of the dike in the first roadcut you pass.  The North Fork of the John Day also cuts through the dike, which is why you see the river suddenly enter a narrow rocky gorge just downstream of Monument. The route follows the North Fork to its confluence with the main John Day at Kimberly.

The North Fork of the John Day enters a narrow gorge at Monument where it cuts through a dike of Columbia River Basalt.

For the rest of the distance to Spray, the ride takes you up and down across the unconformity separating the ancient John Day landscape from the CRB landscape.   The shape of the land here differs markedly depending on whether you are above or below the unconformity.  Below, the river can easily erode the soft John Day ash, so the valley is wide, with a flat bottom that is usually being farmed. Above the unconformity, the CRB make narrow, steep-sided gorges in which you can often see the ledges formed by the alternating hard flow bottoms and soft flow tops.  The road follows the river as it gently descends, so that fact that it keeps crossing the unconformity means that the landscape that preceded the CRB was eroded into valleys and mountains similar in scale to the modern terrain.  The basalt flowed like water, following streams and rivers and filling in valleys and other low spots first until it covered the entire landscape.  When the road passes into basalt, you are crossing an ancient valley carved into the John Day rocks.

Along the way to Spray you will pass several areas of colorful badlands eroded into the John Day rocks, particularly 17.5 and 22 miles from Monument.  Badlands are a specific type of geologic landform that develops on some soft sedimentary rocks in arid areas.  The John Day rocks are fine-grained volcanic ash layers mixed with silt and clay deposited by lakes and lazy rivers.  The material is easily eroded, and quickly removed by rain and wind, so soil cannot form on these slopes.  Plants have a hard time getting established on badlands because of the lack of soil and the fact that the rock erodes with every rainstorm, taking any seedlings with it.

Along this stretch you will also pass by a landslide on the right, 4 miles from Monument.  Here the CRB caps the hill, and its weight was too much for the underlying soft John Day rocks, causing the slope to collapse and deposit a jumble of rock and soil along the road.  Landslides are very common in western Oregon, where abundant rain weakens slopes, but this is one of the few we will pass on this ride.

The route passes a landslide where the soft John Day Formation has collapsed under the weight of the overlying Columbia River Basalt

Two miles west of Kimberly you will pass a large patch of bright white fine ash on the right.  Although this looks like more of the John Day Formation ash at first glance, it is actually ash from a far far younger volcanic eruption.  About 7,700 years ago, a major volcano in the southern Oregon Cascades experienced an enormous explosive eruption. Mt. Mazama blew a column of ash into the stratosphere that blanketed much of central Oregon in thick white ash and pumice, with some ash falling as far away as Calgary, in Canada, over 800 miles from the source. The gaping hole left by this eruption has filled with snow and rain to form the volcanic jewel that is Crater Lake.  The entire area of our Classic route was covered with a s much as a foot of ash, most of which has been washed away or incorporated into the soil, but there are still little deposits like this left in some places, where the ash accumulated in a small valley and was preserved. 

 There are also a few interesting exposures of the CRB along this stretch.  7.5 miles from Monument, the unconformity is visible in a roadcut.  You will see the dark basalt sitting on top of soft white sedimentary rocks, marking a place where the ancient landscape was first buried beneath the waves of hot lava. You will also see well developed columns in the CRB at this cut.  Basalt lava solidifies at about 2000 F, and then the solid rock cools to the temperature of the environment.  The rock must shrink as it cools, and the shrinkage causes networks of fine cracks to develop, often forming long crudely hexagonal columns.

The Columbia River Basalt has well developed columnar jointing in a roadcut 7.5 miles from Monument. Here you can also see the basalt sitting on the older John Day rocks, marking the unconformity

At Spray, the unconformity is easily visible on the western skyline, where you can see the dark rocky slopes of CRB sitting on top of gentler slopes of John Day. The unconformity is tilted to the west here so shortly after leaving spray, the route crosses it again, and remains in the CRB most of the way to Service Creek.  Along this stretch, you will notice that the valley is much narrower and the slopes much steeper, and you will often see the cliff and bench topography that is typical of CRB slopes.  There is a particularly good example around Hoogie Doogie Mountain (That’s really its name!), about 6 miles from Spray.

The unconformity is clearly visible in the long ridge west of Spray
Bench and cliff topography in the CRB near Hoogie Doogie Mountain.

At Service Creek the route leaves the John Day River and starts the long steady climb up Service Creek to the pass.  Three miles up from Service Creek the route crosses the unconformity for the last time for the day, and the ride is in John Day rocks all the way to Fossil.  Since the John Day rocks are under the CRB, you would not expect to encounter them when climbing. The fact that we do means that the ancient landscape had a large mountain here that was never covered by the CRB.


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5 Comments

  1. Wow!! This kind of detail of interpretation of the geology is just spectacular, especially in advance. I’m having a little trouble understanding an “unconformity”. Is that the intersection of the badlands and the CRB flowing over it?

    1. Essentially, yes. It is the surface between the older sediments and the Columbia River Basalt that flowed over and buried the sediments. The surface is not planar, but reflects the topography of the Earth’s surface (the sediments at the surface) at the time the basalt flooded over it.