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Geologic map of the Elgin NE Quadrangle, Lincoln County, Nevada
 
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Title: Geologic map of the Elgin NE Quadrangle, Lincoln County, Nevada

Author: Peter D. Rowley, Lawrence W. Snee, Ralph R. Shroba, F. William Simonds, and R. Ernest Anderson
Year: 2025
Series: Open-file reports
Version: 2025-05
Format: 42" x 30" color map, text, 41 pages
Scale: 1:24,000

This geologic map is one of two geologic quadrangles of the Caliente caldera complex to be published in 2025 by the Nevada Bureau of Mines and Geology (NBMG); two other quadrangles (Rowley et al., 2023a, b) were published in 2023, and more are anticipated. These resulted from mapping and related petrologic, geochemical, and isotopic studies by the authors that were funded by the U.S. Geological Survey (USGS) in the late 1980s to middle 1990s. The mapping was part of a large USGS project named the Basin and Range to Colorado Plateau Transition (BARCO) study in southeastern Nevada, southwestern Utah, and northwestern Arizona. Mapping was to be published by the USGS at detailed (1:24,000) scale, then compiled in 1:100,000-scale quadrangles. The project ended in early 1995 during the USGS Reduction in Force (RIF).

One of the subprojects of BARCO was a study of the Caliente caldera complex and its gold deposits, led by the senior author. Mapping at 1:24,000 scale began at the western end of the caldera complex but only three quadrangles were published (Rowley and Shroba, 1991; Rowley et al., 1994; Swadley and Rowley, 1994). Abstracts cited here and summary reports (e.g., Rowley et al., 1992, 1995, 2001; Best et al., 1993; Hudson et al., 1995, 1998; Nealey et al., 1995; Unruh et al., 1995; Scott et al., 1995a, b) were also prepared before the RIF, with some published after. The seven quadrangles we have completed or will complete were mapped but never published. We also intend to publish with NBMG many 40Ar/39Ar dates by L.W. Snee, most of them from rocks in the caldera complex, that were never released in final form (e.g., Snee et al., 1990; Snee and Rowley, 2000). Funding from the USGS STATEMAP program awarded to NBMG has permitted synthesis and completion of our research in the area and publication of these quadrangles.

The physiography of the Elgin NE quadrangle is dominated by Rainbow Canyon, containing a perennial stream, Meadow Valley Wash, that flows from the northwestern edge to the southern edge of the map area. The small ghost town of Elgin lies at the southern end of Rainbow Canyon, 3.5 km south of the map area. The low range west of Rainbow Canyon is the Delamar Mountains, and the low range east of the canyon is the Clover Mountains, but most rocks on both sides of the canyon are the same, namely subhorizontal tuffs and sedimentary rocks making up the upper part of the Caliente caldera fill. An exception in the Elgin NE quadrangle is an andesitic and dacitic volcanic complex and Cambrian rocks that formed south of the caldera complex but have been displaced along oblique-slip faults into the caldera complex east of Rainbow Canyon. Most of the rocks exposed in the Elgin NE quadrangle are outflow ash-flow tuffs from calderas south and east of the Caliente caldera complex, as well as rhyolite domes, feeder dikes of these domes, and intracaldera tuffs derived from the caldera complex, but beneath these rocks and extending for thousands of meters below the surface are ash-flow tuffs of the caldera complex.

The other map to be published this year, the Caliente quadrangle to the north (Rowley et al., 2025), contains northern Rainbow Canyon, which cuts through most of the same rocks and mountain ranges as in the Caliente quadrangle, exposing four calderas. The Caliente map area includes the attractive town of Caliente (population 990 as of 2020), which serviced and supplied water for the steam engines of the Salt Lake, San Pedro, and Los Angeles Railroad (later bought out by the Union Pacific Railroad) during (1905) and after the railroad was built south through Rainbow Canyon and on to Las Vegas and Los Angeles. The town sits within the caldera complex in the bottom of the canyon in the northeastern corner of the map area, where Newman Canyon joins Rainbow Canyon from the west and the canyon of Clover Creek joins Rainbow Canyon from the east. About 2 km south of town, the Kershaw-Ryan State Park is located along lower Kershaw Canyon, an eastern side canyon to Rainbow Canyon.

Three of the five previously published quadrangles are located to the northwest, north, and northeast of the Caliente quadrangle, respectively: the Caliente NW (Rowley et al., 2023b), Chief Mountain (Rowley et al., 1994), and Indian Cove (Rowley and Shroba, 1991) quadrangles. These quadrangles cover the geology of the northern edge of the Caliente caldera complex and the basins and ranges north of the edge of the complex. The Chief Mountain quadrangle also contains the small Chief gold mining district. Northwest of the Elgin NE quadrangle and west of the Caliente quadrangle, the Chokecherry Mountain quadrangle (Rowley et al., 2023a) contains two calderas of the Caliente caldera complex that underlie the Delamar Mountains. West of the Chokecherry Mountain quadrangle, the Pahroc Spring SE quadrangle (Swadley and Rowley, 1994) describes the western edge of the Delamar Mountains and Caliente caldera complex. The Chokecherry Mountain and Caliente quadrangles also contain the small Taylor gold district. The Ella Mountain quadrangle (partly mapped but not to be published) east of the Elgin NE map area contains the small Pennsylvania gold district. The Eccles quadrangle east of the Caliente quadrangle, which contains three calderas, is slated for publication as part of this project. The Slidy Mountain quadrangle west of the map area, and the Delamar quadrangle west of it are maps intended for future publication; of these, the Delamar quadrangle contains the large Delamar gold district.

Because initial USGS project interests included the origin of metallic minerals, samples were collected for metal geochemistry, including gold analyses. These data are published by NBMG as table 1, included with each of the seven maps, as well as with two of the three maps published by the USGS. Table 2 in each of the seven maps contains previously unpublished isotopic dates from each map area or adjacent map areas. Most rock units are characterized by modal counts, generally 1,000 points, counted on thin sections that number in the many hundreds. Most of the tuffs, as well as some other rock units, are correlated not only by thin section petrography and modal analyses but also by energy dispersive X-ray fluorescence chemistry (using a Kevex instrument; see Rowley et al., 1995).

Suggested Citation: Rowley, P.D., Snee, L.W., Shroba, R.R., Simonds, F.W., and Anderson, R.E., 2025, Geologic map of the Elgin NE quadrangle, Lincoln County, Nevada: Nevada Bureau of Mines and Geology Open-File Report 2025-05, scale 1:24,000, 41 p.

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Original Product Code: OF2025-05