Expedition: dry run

Evidently, the term "dry run" originated with fire departments. It denoted a learning exercise in which the team would stage a fire but, since there was actually no fire, they carried no water.

This expedition was a geologist's version of a dry run. I wanted to see how my geology kit felt on my back. I didn't expect to see any outcrops and wasn't disappointed. Mind you, it was a good outing and, although I didn't see any native rocks, I saw plenty of landscaping.

In an attempt to spot any hint of the Dawson formation, I walked up to the intersection of Arapahoe and I-25, where Rockd indicates that the Dawson formation surfaces out of the plentiful colluvium of the area. So I packed my geology kit northeast about a mile to the interchange.

My first stop was Little Dry Creek Park. We've been there before... it's two blocks from my house. Like most parks, this one is landscaped so there are many tastefully placed boulders laying around. These stones are quite obviously not native to the area, but they do offer examples for beginner geologist's to identify.  This one could be granite. There's lots of quartz, feldspar, and biotite, but there's some pretty folding visible on it's side (you might need to zoom in to see it). That pegs it as metamorphic. I'm going to call it gneiss.

A questing pole is like a third leg (or fourth...some folks use two) to help hikers maintain their balance on the trail. For a geologist, it's primary purpose is to give an idea of scale in photographs. 

This box is on the fence where the Little Dry Creek Trail crosses South Xanthus Street. It marks the area as a storm water monitoring site. When I post stream flow data for Little Dry Creek, this is one place it might come from.

Across Yosemite, just a few steps east, the creek branches out in several directions including this swampy spot.

The Dawson formation is the uppermost of three aquifers underlying Denver. Since the area is high desert, it doesn't get a lot of rainfall and the aquifer isn't very productive but it does feed many of the streams.

The rock of the Dawson formation is mostly sandstone with some siltstone. It's the southern extension of the Arapahoe formation that is the primary bedrock under Denver.  Impermeable mudstones and shales under the sandstone hold water in the sandstone, which is why it's an aquifer.

The area around Yosemite has some nice views of the Rockies. The higher you are, the better your perspective, and Yosemite and the parallel interstate highway are at the summit of the eastern rim of the South Platte River valley.

These distant views compliment close-up geology well. For instance, Waterton Canyon is at the far left of this photograph. When you're in the canyon, it's hard to tell whether the rock walls rise to spires or if they are the shoulders of mountains. This view shows the later to be the case. It displays the structure of the Front Range and the relations of its parts.

At the top of the ridge is the Regional Transportation  District light rail and Interstate 25. Just to the north I-25 crosses over Arapahoe Road at an interchange. These types of construction usually require a lot of land shaping, which means that I didn't expect to see much of the Dawson formation or any other native stone in my small expedition.

I do have a soft spot for railroad ballast, the gravel used to cover the beds of train tracks. When I was a kid, I spent a lot of time on railways. Nowadays, they discourage "visitors" because injuries on railways can be expensive. Thus, the fence.

Ballast is usually crushed granite, often large grained granite that has nice crystals of feldspars, epidote, amphiboles, and other minerals. Of course, they don't tell you much about the place where they're found because they're from somewhere else.

This is the kind of "outcroppings" to expect at Interstate exchanges. Colorado, at least, tried to make their highways attractive, in a landscaped, skateboarding park sort of way. But nothing visible is native.

The boulders used for landscaping can be interesting. 

Much of it is granite like this big chunk of white stone.

But, to supplement the earlier photographs of metamorphic and igneous boulders, there was this big piece of mudstone, which may have even been taken from the locality. Notice the banding in the side.

The ripples on the surface indicates that this stone is a top surface of a layer of mud laid down in an aquatic environment.

The Dawson formation is composed mostly of sandstone but includes some mudstone. The layer is about 50 to 100 million years old. During that period, Colorado was under a shallow, inland sea.

On the way back home, I had a few groceries to pick up at the Arapahoe Marketplace Shopping Center. This fellow stands outside.

The sculpture is interesting...a symbol of wild nature made of found materials.

So, this was a dry run to check out the portability of my geology kit. As for the geology, I had no expectations and I didn't get to actually use the kit (except for the trekking pole). But I'm pretty happy with the kit. It only weighs about 4 pounds and fits nicely in my backpack.

The components, from left to right, are a Modular organizer, Husky small parts organizer, Promaster trekking pole, Ozark Trail (Walmart) backpack, and Moto E5 Cruise Android phone.

The Modular organizer carried labels and information pamphlets along with a host of tools. I have a geologist's pick (somewhere) but in the interest of portability, I opted for a multi tool hammer and two chisels (one blade and one conical tipped) for chipping rocks. A set of files are also useful for getting crystals and fossils out of their matrix and for testing hardness (Mohs hardness 6.5). The other multi tool provides, among other things, an accessory knife.

Dental cleaning tools, tweezers, and paint brushes are useful for fine work in cleaning up samples.

I carry my smartphone clip-on microscope to make photomicrographs for the blog and a small beam balance. The spot plate is for quick chemical assays. I can throw small bottles of reagents into the mix as needed. And a ruler and vernier micrometer is there for fine measurements.

I keep my smartphone in a wallet type holder with lots of pockets. Along with a few personal items, There's a note pad, a couple of Fresnel magnifiers, a credit card sized multi tool with cutting edges, a rulers, and some survival information. I also hang a pen, flashlight, and hook/stylus on the lanyard. These are my everyday at-home tools.

Along with the Rockd app, my phone stores the MC50 Programmable Calculator and several measurement tools: AllTrails, Physics Toolbox Pro, the Arduino Science Journal, and the Dioptra theodolite app.

Like astronomy, geology makes a lot of use of angle measurements to describe landforms. Dioptra is the best tool I've found for that.

The Husky organizer is nicely waterproof. I carry my incidental hardware in it...sample containers and padding, Mohs hardness materials, streak plates, magnifiers, microscope slides and cover slips, droppers, a dropper bottle with 10% v/v hydrochloric acid, and anything else I might need on a particular outing.

I also pack some tools in the Husky...a tape measure, IR thermometer, ultraviolet flashlight, and a reflection microscope (the clip-on microscope I carry is a transmission scope.) I also carry a surveyor's compass. It does the same things the Dioptra app does but sometimes the manual operation is more practical than the digital instrument.

It's also a good idea on a geology outing to throw relevant field guides (both general and about your local area) and a topographic and geological map of your area - notice that the Rockd app provides both - into your pack.

So that's my set-up. Yours might be different according to your preferences, finances, or just what you have at hand. For geology on the trail, though, it should be light and I very consciously lean toward inexpensive.

Two of my favorite resources are:

American Science and Surplus

and

Home Science Tools

I also like to cannibalize inexpensive science kits. My IR thermometer came from a Science Wiz kit.

Science Wiz

If you look around, you can probably find most of what you need for geology field work.

How deep is my valley?

Sounds like one of those period dramas, doesn't it?

Of course, I'm still just going on about the Little Dry Creek valley a couple of blocks over from my house.

I've mentioned that the mountain streams in the Rockies are very different than the ones I knew as a child back east. Little Dry Creek, on the other hand, looks very familiar, but all streams have their own personalities. 

On the last walk down the hill, I took some side trips from the main road that parallels the creek, Arapahoe Road, down to the creek to get an idea of the cross sections. You remember that I took one elevation profile down Uinta Street a couple of blogs ago. I supplemented that with three others starting near the rim of the South Platte River valley and stopping at the western end of Walnut Hills, Quebec Street.

Little Dry Creek Park is near the head of the valley where the creek emerges from a culvert under Yosemite Street. On the other side is just storm drainage channels.

Here the creek cuts a shallow channel surrounded by a wide plain. In about 250 feet, there's only a rise of about 10 feet to the surrounding residences. I figure that the plain was carved by the creek because the rise up to the residences have been reinforced by stone to prevent further erosion in that direction.

The headwaters of Little Dry Creek is just building up energy and volume here. There's enough flow to have cut a shallow notch but it looks like it has meandered in the recent past. I doubt if there has been a lot of flooding. The flow has been erratic as shown by water level readings over the last year.

I was in the area in 2020 and 2021 and the maximum flow of 5 cubic feet per second was not enough to flood the creek's banks.

Much of the variance is due to snow melt and occasional spring rains. This data is from the area west of Walnut Hills where the creek passes under Arapahoe Road.

As the creek builds up energy and volume, it cuts a deeper valley with less meandering.

At Uinta Street, the valley drops into the hilly section behind Walnut Hills Elementary School. 

The elevation difference between the top of the hill to the bottom, at Spruce Street, is about 70 feet. The ridge passes through Walnut Hills. It's very visible on Arapahoe.

I would think that it's older than the creek...maybe a bump in the Dawson formation that appears as outcrops northeast and south of Walnut Hills. Regardless, the creek has cut deeply through the ridge. The whole length of the creek has erosion prevention features like small weir dams and boulders that have been moved into the stream bed so the back cutting has been slowed considerably.

I like trying to visualize what different places might have looked like before buildings were there. I wonder if there was a Cascade here.

At the bottom of this grade, Spruce Street crosses the creek.

The creek begins to meander again and there's a wider plain. They're also deeper banks. 

In 0.2 mile, the walk down from Arapahoe only descends about 40 feet. 

The creek begins cutting some fairly deep banks, some about six feet, close to my last stop, Quebec Street at the western boundary of Walnut Hills. These show some nice soil profiles, so I should be coming back later.

Here the valley is broad and the gradient into it is gradual. Over 0.2 miles, the descent is only about 30 feet. On the other side of Quebec, the valley begins deepening again, as shown in the photograph above shot through a fence. (The Little Dry Creek Trail pulls away from the creek for a ways to follow sidewalks around a residential area.)

I have only been looking at the creek valley in Walnut Hills neighborhood. The valley actually extends further on the other side of Arapahoe Road. The rim peaks about a half mile from the creek at Fiddler's Green. Little Dry Creek has slowed down considerably due to erosion controls installed with the residences of Walnut Hill, but it has evidently been much more active in the past 

Now, a few words about the AllTrails app. It's a great tool for measuring distances and elevations but it's not terribly intuitive, so let me give you a few tips. My version is 14.3.1 of AllTrails Pro and I use it on an Android phone version 8.0.0.

Use the Navigate command (the middle button on the toolbar at the bottom of the AllTrails window) to get to the tools. Choose "Start without a route" and choose an activity. Hiking or walking is good. Then just press the start button. When you reach your destination, press and hold Pause and the app will ask you if you are finished. Press Finish. It will ask you how your trip was. On my Android, the app has frozen at this point but, if you close the app and restart it, you will find your data saved in History. Later versions may fix this glitch and it may not happen on other operating systems.

Nevertheless, AllTrails is an excellent app to measure the shape of your landscape. There is a free version. The Pro version isn't expensive and provides more reporting features.

Before begining a study outside, it helps to get a lay of the land. What does your neighborhood look like? What does it contain - rocks, plants, animals, attractions, hazards, streams, hills... outcroppings,