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BUTTerwICK & dANIeL: FLOrA OF SOUTHerN BLACK MTS., ArIzONA 271<br />
Most of the flora area is public land administered by the U.S. department of Interior’s Bureau<br />
of Land Management (BLM), and includes two wilderness areas: Mount Nutt wilderness, a 112-<br />
sq. km (27,660-acre) area north of Mohave Co. 10 through Sitgreaves Pass, and warm Springs<br />
wilderness, a 455-sq. km (112,400-acre) area at the southern end of the Black Mountains (U.S.<br />
department of Interior 2016a, 2016b). Although land ownership is primarily BLM, there are some<br />
private and state of Arizona holdings within the flora area, particularly in the town of Oatman and<br />
along Mohave Co. 10 (Oatman road) in Sitgreaves Pass. The Black Mountains are known for their<br />
mineral resources. Numerous mines throughout the Oatman mining district produced significant<br />
quantities of gold (2.2 million troy oz) and silver (0.8 million troy oz) between 1897 and 1942<br />
(dewitt et al. 1986).<br />
The present study was undertaken to document the botanical resources of the southern Black<br />
Mountains. Based on Moore and Cole (2004), this is the first published flora for a region within<br />
the Mohave desert of Arizona. Certain plant communities such as great Basin Conifer woodland<br />
and both desert Oasis woodland and Streamside Marsh at perennial springs are very restricted in<br />
the Black Mountains, and thus are particularly vulnerable to increased warming and drought anticipated<br />
from climate change in the region (garfin et al. 2014). Our results can serve as a basis for<br />
examination of future changes in the flora of this range and other areas of Mohave desert in southern<br />
Nevada and southeastern California.<br />
TOPOgrAPHy ANd geOLOgy<br />
The Black Mountains are located in the Basin and range Physiographic Province (wilson<br />
1962) and form a north-northwest-trending mountain range with wide valleys on each side—Sacramento<br />
Valley to the east and Mohave Valley to the west. The range is known for its extremely<br />
rugged terrain. The northern portion of the flora area has a total relief of about 914 m (3000 ft).<br />
The highest points in the flora area are an unnamed peak (“Benchmark Nutt”) at 1590 m (5216 ft)<br />
and Mt. Nutt at 1543 m (5062 ft). These peaks are surrounded by precipitous cliffs, small mesas,<br />
steep and rocky slopes, and several steep-walled canyons such as grapevine Canyon, Cottonwood<br />
Canyon, and several unnamed canyons (gray et al. 1990b). An area that is underlain by Proterozoic<br />
granite, schist, and gneiss is exposed near Arizona Hwy. 68 between Thumb Butte and Secret<br />
Pass Arch (Nations and Stump 1996). However, most of the remainder of the northern portion of<br />
the flora area is overlain by a variety of Tertiary volcanic rocks including rhyolite, andesite, dacite,<br />
basalt, and tuff (gray et al. 1990b). In fact, most of the Black Mountains, including our flora area,<br />
are volcanic in nature and in this respect differ from surrounding mountains and basins in Arizona,<br />
California, and Nevada—in effect forming a geologic/edaphic “sky island” in the Mohave desert<br />
of western Arizona (elvin et al. 2013). west of the main mass of the mountains is a complex of volcanic<br />
and granitic hills in the vicinity of Pheland Butte, Cathedral rock, Hardy Mountain, Finger<br />
Butte, and Thumb Butte (Nations and Stump 1996; U.S. department of Agriculture 2016).<br />
Meadow Creek, a major east-west-trending tributary of Sacramento wash, forms a prominent<br />
divide in the southern Black Mountains. Mohave Co. 10 (Oatman road) east of Sitgreaves Pass<br />
generally follows Meadow Creek. The southern portion of the flora area, south of Meadow Creek,<br />
is dominated by Black Mesa (Fig. 2), a northwest-trending plateau of Tertiary basalt (gray et al.<br />
1990a). The summit of Black Mesa ranges in elevation from approximately 975 m (3200 ft) to 1158<br />
m (3800 ft). Topographic relief is abrupt particularly along the east front of the mesa with drops in<br />
elevation of 305 m (1000 ft) or more to the surrounding pediment, alluvial fan, and piedmont surfaces<br />
that slope gradually across the Sacramento Valley toward Sacramento wash. The mesa is<br />
deeply incised by warm Springs Creek and several unnamed tributaries (gray et al. 1990a), and it
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