Across the Alluviums

From here, it’s time to go on an excursion. I like to hike in Roxborough State Park, so we’ll travel out there and look at the geology along the way. As we go, we'll drive across the alluviums that sit underneath the metro area. All the alluviums that form the surface geology of the Denver area are outwash from the Colorado Rockies that still rise above the plains, not the ancestral Rockies, which are long gone.

This diagram, copied from "Guide to the Geology of Colorado" shows a cross section of the alluvial terraces in the Denver area. I-25 and the South Platte, for example run in the little trough on the far left of the diagram, so as we view the cross section we are facing south. The type is too small to be scanned legibly, but to get the idea, know that each terrace is an alluvium from a different time era. In general, the younger alluviums are to the left, and the older ones are to the right. Bedrock (not shown on the diagram) can be found peaking through the alluviums, like at Roxborough, or to the far right against the mountains, like the Flatirons in Boulder.

This first picture is the corner of Kalamath and Colfax. Piney Creek Alluvium(1500 years old or so) is underneath the street here.

This next picture is at 2nd and Kalamath. A mammoth tooth was found here. Fossils of extinct mammals are often found in alluviums in the Denver area.

This picture is perhaps what the alluvium looks like, a mix of gravel and sand.

Here is the South Platte, taken from Santa Fe going south in the Littleton area. Post-Piney Creek alluvium is along the main channel of the river. Post-Piney Creek alluvium is an alluvium similar to Broadway alluvium, but Broadway alluvium is much older, about 10,000 years old or so.

Here is some more Eolian sand blown from the South Platte River. Look at the rabbitbrush and sandsage in the second picture, telltale signs of sand beneath the soil.

This picture, looking to the west of Highway 85 (Santa Fe), shows terraces of the South Platte.

This is a picture of Broadway alluvium on the road to Louviers. We are getting closer to East Plum Creek.

This alluvium here is the Louviers alluvium, and comes from weathered Pikes Peak Granite.

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Directions (from Library):

Continue on 14th Avenue east.

5.2 left on Lincoln

5.3 left on Colfax

6.1 left on Kalamath: Post-Piney Creek Alluvium

Continue south on Kalamath.

7.7 2nd and Kalamath. Mammoth tooth found underneath.

Continue on Kalamath. Kalamath becomes Santa Fe (Highway 85)

12.8 South Platte on right. Continue on Santa Fe.

20.9 Sand dunes and shrubs on left.

21.2 Terraces of the South Platte on left.

25.7 turn right to Louviers

26.9 Broadway Alluvium on right. Follow road across bridge and into Louviers. Stay on road to the left out of town. Road goes to left again back towards creek.

28.4 Louviers alluvium. U-turn. Go back to Highway 85

30.3 turn left on Highway 85.