Unit 851, Colorado

Elevation ranges from approximately 6,025 feet near Trinidad (eastern low end along I-25) to 14,047 feet on Culebra Peak along the western Sangre de Cristo Divide — a vertical relief of roughly 8,000 feet. Terrain transitions from moderately steep foothills and mesa country in the east through steep, heavily timbered ridges and deep canyons in the mid-elevations to alpine tundra and talus above treeline. Bosque del Oso SWA itself sits at 6,937 to 8,938 feet and is characterized by rocky slopes, tight canyons, and scrub-covered benches. The South Fork of the Purgatoire River drains east through the core of the unit.

Public land is approximately 12% of the unit — almost entirely state land, with roughly 2,112 USFS acres near the northern unit boundary and Bosque del Oso SWA comprising the bulk of state holdings. Bosque del Oso SWA (30,000 acres, Las Animas County; GMUs 85 and 851) is the primary public hunting venue. It is reached via Colorado Highway 12 approximately 25 miles west of Trinidad; entry roads are signed south of the highway between the communities of Weston and Zamora (west entrance 6 miles east of Stonewall, east entrance 9 miles east of Stonewall). Within Bosque del Oso, parking is from designated areas only and roads are closed to hunters — access to hunting areas is on foot. Oil and gas infrastructure is present on the property. The remainder of the unit (~88%) is private land. Two Ranching for Wildlife (RFW) properties operate within the unit: Tercio Ranch (25,000 acres), located 6 miles south of Stonewall near the New Mexico border, with elevations from 8,000 to 10,000 feet and habitat including ponderosa pine, Douglas fir, open meadows, and cottonwood bottoms along the South Fork of the Purgatoire River; and Hill Ranch (63,200 acres), located approximately 15 miles west of Trinidad on Highway 109, with elevations from 6,600 to 13,700 feet. RFW ranches offer limited licenses distributed through the Colorado draw, with a portion allocated to resident hunters. Other private ranches in the unit require landowner permission or outfitter access. Bosque del Oso SWA is open for public access May 1 through November 30; December 1 through April 30 it is open only to licensed big-game and spring turkey hunters and one non-hunting companion. The CPW Pueblo Area Office (719-561-4909) manages the SWA.

Land cover is approximately 56% evergreen forest, 20% shrub/scrub, and 10% grassland. Low- to mid-elevation slopes support pinyon-juniper woodland and extensive Gambel oak brush fields interspersed with cactus and native grasses. Ponderosa pine and Douglas fir dominate north-facing slopes and mid-elevation ridges from roughly 7,000 to 9,500 feet. Aspen groves occur in moist draws and transition zones. Spruce-fir forest covers upper slopes approaching treeline. Alpine meadows exist at the highest peaks along the Sangre de Cristo Divide. Riparian cottonwood-willow corridors run along the South Fork of the Purgatoire River and its tributaries. The dense, low-canopy scrub oak and pinyon-juniper in the foothills creates thermal cover that serves as critical winter range for elk and mule deer.

Elk are the dominant big game species and primary draw for hunters. The unit is a well-documented wintering ground: elk summer on the high Culebra Range and adjacent private ranches, then migrate downslope to the scrub oak and pinyon-juniper foothills and into Bosque del Oso SWA during fall and winter. By late rifle seasons (3rd and 4th), elk concentrations — including bulls pushed off adjacent private land by hunting pressure — move onto the SWA in significant numbers. Mule deer are distributed throughout the unit and follow a similar elevational migration, also using the SWA as winter range. White-tailed deer occur locally in riparian zones at lower elevations. Black bear are present across the unit, particularly in scrub oak and mixed forest zones during summer and fall; the SWA is named Bosque del Oso (forest of the bear) for its historically high bear population and backpackers are required to use bear-resistant food storage. Mountain lion inhabit the unit year-round, following deer and elk herds through canyon and rimrock country. Turkey (Merriam's) are present in ponderosa pine and oak-brush habitats. Pronghorn may occur on the lower grassland fringes along the eastern edge near the I-25 corridor. The elk rut begins as early as the first week of September and runs through approximately October. The mule deer rut begins in late October and can extend through late December.