The Sulphur HMA comprises approximately 265,676 acres of public and other land. The HMA is located in western Iron, Beaver, and Millard counties, Utah approximately 50 miles west of Minersville, Utah in the Indian Peak and Mountain Home Mountain Ranges. The elevation ranges from 9,790 feet on top of Indian Peak to 6,000 feet in the valley floors.
Average annual precipitation in the Sulphur HMA ranges from 8 to 15 inches a year, depending on elevation. In 2005 the precipitation was near 110% - 130% of normal in the HMA. In 2000 and 2006, annual precipitation was near normal. However, because of the timing of precipitation, it had little effect on the recovery of vegetation or the recharge of springs and seeps. In 1999, 2001, 2002, 2003, 2004, 2007, 2008, and 2009 drought conditions and below normal precipitation occurred, with 2002 and 2003 being severe drought years. Vegetation, springs, and seep continue to struggle to recover from so many years of below normal precipitation. During the 2010 water year the precipitation was near normal, with good precipitation in the spring.
The Sulphur HMA supports multiple vegetation types including: Aspen, Mountain Fir, Spruce-Fur, Mountain Shrub, Pinyon-Juniper (PJ), sagebrush, grasslands, and salt desert shrub. The PJ woodland type dominates the HMA and is very dense with minimal understory forage. Open areas outside the PJ canopy are dominated by big sagebrush with Indian ricegrass, wheatgrass, bluegrass, and squirreltail grass as the primary forage species.
Available water within the HMA is the limiting factor regarding these horse populations. Water is limited to isolated springs and man-made developments that supply water to permitted livestock, wildlife, and wild horses. Several springs primarily used by wild horses, were dry during the summers of 2000, 2001, 2002, 2003, 2004, 2007 and 2008 forcing animals onto winter ranges and into areas outside of the HMA traditionally unoccupied by horses. Most water sources have produced at average levels allowing for normal use of the summer and winter ranges this year. A small number of horses (15-25 head) did move outside of normal use areas due to range improvements (troughs, well pumps, and pipeline) being in need of repair.
The Appropriate Management Level (AML) for wild horses within the HMA is 165-250. The AML was established in the Pinyon Management Framework Plan (MFP) Rangeland Program Summary ROD 1983, the April 1987 Warm Springs Resource Area RMP/ROD, and the Sulphur Wild Horse Herd Management Area Plan 1987, following an in-depth analysis of habitat suitability and resource monitoring and population inventory data, with public involvement. The AML upper limit is the maximum number of wild horses that can graze in a thriving natural ecological balance and multiple use relationship on the public lands in the area. Establishing AML as a population range allows for periodic removal of excess animals (to the low range) and subsequent population growth (to the high range) between removals.
The current estimated population of wild horses within the HMA is estimated at 276 head. This estimated number is based on an aerial survey direct count population inventory conducted in February 2008 with an estimated count of 80% of the total population based on coverage, weather, terrain, tree cover, snow cover, and knowledge of the HMA/horses, which estimated the population at that time to be 435 head of wild horses. The 2008 foal crop was added to the estimated population, 333 head that were removed in the November 2008 gather were subtracted and the 2009 and 2010 foal crops were added to formulate the current estimate population. The foal crop and survival of those foals increased the estimated wild horse population within the HMA by 20% each year between March 1 and July 1. The current estimated population of 276 wild horses is 110% of the upper AML.