Wheeler Geologic Area

Title: Wheeler Geologic Area

Author: Sandra Mark

Publication: The Outcrop, October 2011, p. 4, 7

Article Type: Lead Story

 

10.1 Outcrop_Leadstory 1

Wheeler Geologic Area is a place of spectacular beauty and compelling geology. It was the first National Monument in Colorado, from 1908 to 1950 (when it was deemed too remote to deserve the designation). Geologically impressive, it is within the central San Juan caldera cluster, among the largest in the world. And for all its remoteness, it is within a wilderness area but accessible by a road as well as a hiking trail.

The Wheeler Geologic Area (Wheeler) is located in southwestern Colorado, about 8 miles ENE of Creede. It was incorporated into the La Garita Wilderness Area when that was created in 1964. La Garita means “The Lookout” in Spanish, and might refer to the 14,014 foot San Luis Peak.

The area is named after Captain George Wheeler, who surveyed the region for the Army in 1874. It was included in the Wheeler Survey; part of an ambitious plan supported by the U.S. Congress to map the country west of the 100th meridian at a scale of 8 miles to the inch. The Powell Survey and the King Survey were also part of that mapping project, which continued until 1879 when their work, along with the Hayden Survey, provided a legacy for beginning the U.S. Geological Survey (USGS).

The USGS has published a number of reports on the calderas of the San Juan Volcanic Field of Southwestern Colorado. Notably, Peter W. Lipman has authored or coauthored research spanning 40 years, most recently a large geologic map of the area (which includes Wheeler). Lipman describes the San Juan Mountains as a large erosional remnant of a composite volcanic field that was created during Oligocene time. It is comprised of a series of caldera complexes, each with associated eruptive cycles. The enormous La Garita caldera and its Fish Canyon Tuff defines the overall geometry of the central caldera cluster. Wheeler is included within that cluster in the San Luis Caldera Complex, which is the source of three successive ash-flow tuffs that are exposed at the site (Lipman, 2006). Please refer to the accompanying photo. The pinkish rocks in the foreground and middle left are the Rat Creek Tuff. The grayish rocks to the right center and upper left are the Cebolla Creek Tuff. The dome-shape at the top and layers to the right of it are Nelson Mountain Tuff. Isotopic ages range from 26-27 Ma.

History buffs will be interested to know that Wheeler is about 7 miles WNW of the site of Christmas Camp occupied by the ill-fated Fremont Expedition of 1848-49. Charged with the goal of finding an all-weather railroad route through the central Rocky Mountains, they were plagued by winter storms and lost 10 of the 35 men. Two personal expeditions to visit the exact site of Christmas Camp have been unsuccessful both times, even armed with GPS technology and following experts with the Rio Grande County Museum. This sort of experience lends a sense of mystery to this beautiful, remote area.

Plan two days to visit Wheeler, whether driving or hiking. From Highway 149, take Pool Table Road (Forest Service #600) a 2-wheel drive dirt road, just north of Wagon Wheel Gap. The trail head (both road and hiking) is about 10 miles from the highway at Hanson’s Mill (just a sawdust pile remains). The 4-wheel drive road is grueling: high clearance and great courage are required. It is about 10 miles to the boundary of Wheeler (the Forest Service claims 14 miles) and it takes about 4 hours in a vehicle, less for an ATV. The hiking trail is 7 miles and it is said that hikers will arrive before road travelers. At the Wheeler boundary, a 0.4 mile hike leads to the 2.8 mile Wheeler Geologic Area Loop Trail. Hikers taking the trail counter-clockwise (left at the intersection) will arrive at the view shown in the photo more quickly. Hikers doing the entire loop will approach 12,000 feet in elevation and will be rewarded with breath-taking views of the region. There is primitive camping at Hanson’s Mill and the Wheeler boundary. Of course good maps and knowledge of the weather forecast are essential; the roads are impassable when wet.

The journey to Wheeler Geologic Area is not an easy thing but well worth the effort, especially for geologists.

References
Lipman, Peter W., 2006, Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado, USGS Geologic Investigations Series I-2799.

Websites: Rio Grande National Forest, Rio Grande County Museum, Sangre.com, USGS, Wikipedia (calderas, La Garita, Wheeler)

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