Route 114A

.TOURING

COLORADO GEOLOGY

Route 114 Gunnison to Saquache
(part 1)

Just east of Gunnison about 8 miles along Highway 50, Colorado 114 heads south to Saquache. The road is fairly narrow (compared to Hwy 50) and rough even though it is paved, but makes for an enjoyable drive with lots of geology.
	As I said, turn south onto Hwy 114, first crossing Tomichi Creek, then Cochetopa Creek, you travel fairly straight for about 2 miles before entering a relatively narrow canyon with a very curvy road which follows Cochetopa Creek. Most of these rocks are dark metamorphic schists. The foliation is almost vertical and creates some very striking outcrops. At Mile Marker (MM) 5, you cross the Cochetopa Creek again. The rocks through this area continue to be dark metamorphic schists. At MM 8, we leave Gunnison County and enter Saquache County. Throughout this area small uranium mines of the 1950's can be found.
Between MM 13 and 14, the rocks change to red granite (Cochetopa Granite). Exposures along the road are quite dramatic with steep cliffs and interesting jointing patterns. There are a number of small pulloffs along the canyon and creek.

	By MM 18 you leave the canyon and enter into a broad valley which is strikingly different from what we were just driving through. This broad valley is actually a caldera, one of 15 that have been identified in the San Juan Mountain region. Outcrops of white volcanic tuff occur along the road. The caldera is about 24 km across formed during ...
Off to the right (south) is the very prominent Cochetopi Dome. As you start to climb out of the caldera, the rocks change from the very white tuffs to reddish-brown tuffs, some filled with large rock fragments reminiscent of the West Elk Breccia although the fragments are much smaller in size.
	As you continue up toward Cochetopa Pass (3093 m), the tuffs alternate with basalts some of which show some very nice columnar structures. These "columnar basalts" are formed due to cooling and contraction of the basalt as it cooled. The joints are formed perpendicular to the cooling surface; their size (diameter) is interpreted to be related to the rate of cooling. The faster the basalt cooled, the smaller the columns. These are relatively small (5 to 6 inches in diameter) compared to some much more notable columnar basalts such as the Devil's Postpile in California, Devil's Tower in Wyoming and the Giant's Causeway in northern Ireland. The best are between MM30 and 31 and again on the other side of the pass between MM 33 and 34.
This whole area is quite complex with lots of different episodes of eruptions expressed by different tuffs, some air-fall others water-laid along with mudflows and biotite-hornblende dacite.
	At MM 37, at the intersection with Road 31CC to North Park and Spanish Creek goes off to the left. Here are some really bizarre outcrops of the Fish Canyon Tuff. The Fish Canyon is a crystal-rich quartz latite ash-flow. The structure referred to as "beehive" is probably due to crude wide columnar jointing and wavy compaction layering.