My geology laboratory will be the Little Dry Creek valley in the Walnut Hills neighborhood in Centennial, Colorado. I have been assured that there is, in fact, not a single walnut tree in Walnut Hills. Also, I have never seen Little Dry Creek without water flowing through it. And it is "little" not because of it's size. It was named after the same engineer from New Hampshire, Richard Sullivan Little, that Littleton, Colorado was named after. Little settled in the area with his family in 1862. The town of Littleton is about 15 miles due west of Walnut Hills.
Two creeks have sculpted the Walnut Hills area, Little Dry Creek and Willow Creek. The soil is deep and soft so the creek valleys are fairly deep and steep. They are tributaries of the much larger South Platte River valley in which the Denver metro area is located.
The creek begins as runoff from the area just east of Walnut Hills and is tracked by the Little Dry Creek Trail, part of the Centennial Connector Trail, which parallels it throughout the neighborhood. I take the trail often on trips to the several shops in the area, so I have plenty of opportunities to study the area.
In general, road cuts, newly graded dirt roads and other architectural features that clear dirt off the rock below are a geologist's friend...not necessarily here.
It is an urban area, which means that I will have to be careful to distinguish between the actual geology and landscaping. Granite is not indigenous to this area so the rocks in the above photo were brought in. Here is a picture of the natural materials that inhabit the area.
The dirt and mud goes pretty deeply.
That doesn't sound too interesting, geologically, but I think you'll find that not to be the case. The place in the photo is at the western border of the neighborhood and is the only place on Little Dry Creek that shows a well defined soil profile, so I will certainly be coming back here.
On a walk down the trail to a local grocery, I used my AllTrail app to get an idea of the shape of the valley. I started at the eastern border of the neighborhood and walked to the western border. Here's the map and elevation profile.
Over 1.2 miles, the creek drops about 130 feet. Of course, this is the elevation profile of the trail, but the trail begins and ends at close to the elevation of the creek. The grade is pretty much linear. The hump at mile 0.6 is where the trail runs up the shoulder of the valley above the creek.
On the return trip, I walked up the main road and cut down Uinta for a cross section of the valley down from the rim. Here's an elevation profile of that.
I'll take some other cross sections later. Of course, they change from the top of the valley to the bottom. There are five places that roads cross the creek on the neighborhood.
Notice above that AllTrails provides topographic maps. The gray lines in the above maps are contours. Google Maps, Google Earth and the Rockd app also gives you topographic maps. When hiking, a topographic map is important. When exploring the geology of an area, they are necessary. A topographic map shows you the shape of the land.
Rockd also provides geological maps of areas. Those show you the kind of rocks and history of an area. I'll look at what the Rockd app has to tell me about Walnut Hills in the next blog.
It's possible that you have been walking around your home territory for years without considering what's under your feet. The next time you're out, look around and ask yourself how the land became the way it is. What were the shaping forces? What are the rocks and dirt like and why are they like that?
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