One of the great Blue Highways in Colorado is CO 14 trending from Teds Place, northwest of Fort Collins, westward to Walden. Teds Place is situated in a valley between the Cretaceous Dakota Formation (forming the prominent “Dakota Hogback”) and the ~1.7 Ga Precambrian metamorphic rocks of the Front Range. The valley contains rocks of Pennsylvanian, Permian, Triassic and Jurassic age but they are not well exposed.
CO 14 generally follows the Poudre River, a Blue Ribbon trout stream, and travels through some of the most spectacular scenery in the state. Immediately after leaving Teds Place the road plunges into the canyon of the River and its exposures of Precambrian rocks. This lower section of the canyon is unglaciated and therefore has a characteristic “V-shape”. The upper reaches of the canyon have been glaciated and visitors will notice a distinct difference between this upper “U-shaped” section beginning about Home Moraine (~mm 85). A glacial terminal moraine also backs up Chambers Lake near the summit of Cameron Pass.
Also near Cameron Pass Larimer Co Rd 103 takes off north and follows the Laramie River to the WY-CO state line. Since the road is graveled rather than paved it could not qualify as a Blue Highway but would be listed as what, a Blue Back Road? The narrow river valley is bordered on the west by the Medicine Bow Mountains and on the east by the Front Range. Both of these ranges have bounding thrust faults.
Digital satellite image looking north from Chambers Lake along the course of the Laramie River.
Map showing principal uplifts exposing Precambrian rocks in Colorado. Note Front and Park ranges extending into Wyoming. Map from Sims and others, 2001.
In climbing around on the Medicine Bows I noticed a few glory hours and the rocks seemed not very interesting, certainly not for collecting! It is my understanding that a few early prospectors were out looking for copper. However, when the state line is crossed there are several old gold/silver mines in the Wyoming section.
The narrow valley of the Laramie River in Colorado exposes a section of Cretaceous rocks (and probably some of the basin filling Tertiary North Park Formation) that seems accidental and trapped between the two mountain ranges. I prospected the Pierre Shale but was unsuccessful. I was able to locate a few outcrops that contained numerous Cretaceous clams, mostly inoceramids (extinct clams quite common in the Mesozoic). Without a detailed geologic map I was a little uncertain as to exact location in the stratigraphic column; however, I suspect they were from the Cretaceous Carlile Formation/Group.
Klein, T. and K. Kellogg, 2011, Central Colorado Assessment Project: http://esp.cr.usgs.gov/research/central_colorado/index.html
Sims, P.K., V. Bankey, and C.A. Finn, 2001, Preliminary Precambrian basement Map of Colorado--A geologic Interpretation of the Aeromagnetic Anomaly Map: U.S. Geological Survey Open File Report 2001-0364.