The Leon quadrangle covers about 58 square miles in Eagle and Garfield Counties, which are in west-central Colorado, and includes the towns of Basalt and El Jebel. Includes cross section; map unit correlation; shaded-relief map with geology overlay; and booklet of extended descriptions of map units, geologic setting, structural geology, economic geology, and references. Note that MS-40 is the digitally produced, full color version of the original black and white open-file report OF-98-03, as further discussed below. 26 pages. 1 color plate (1:24,000). Digital PDF download. MS-40D
This map and accompanying booklet were slightly modified from the original OF-98-03, incorporating changes to some mapped units based on the updated conceptual model of widespread late Cenozoic evaporite collapse in the region. Mapping of this and nearby quadrangles has contributed to further understanding of the Neogene salt related deformation and geomorphology in an area of active salt tectonism. Also new is the correlation of Neogene basaltic rocks based on 44 samples of volcanic rocks collected from the Leon quadrangle during a collaborative investigation subsequent to the publication of CGS OF-98-03. These samples were analyzed and correlated using geochemistry, 40Ar/39Ar geochronology, magnetostratigraphy, paleomagnetism, and petrography.
From the Author’s Notes:
The Leon quadrangle covers about 58 square miles in Eagle and Garfield Counties, which are in west-central Colorado, and includes the towns of Basalt and El Jebel. Colorado Highway 82, which parallels the Roaring Fork River Valley, crosses the southwest corner of the quadrangle. Basalt Mountain, the highest peak in the quadrangle, towers over the balance of the quadrangle. Most of the land in the northeastern and east-central parts of the quadrangle is public land administered by the White River National Forest. Private land that historically was used mainly for ranching, but which now is rapidly developing, lies along the Roaring Fork River valley and in the northwest part of the quadrangle. The remainder of the quadrangle is public land managed by the Bureau of Land Management. The 1:24,000-scale topographic base map of the quadrangle was first published in 1961 and later updated in 1987 using aerial photographs taken in 1983.