Unit 91, Colorado

GMU 91 is entirely low-elevation plains terrain, ranging from approximately 3,600 to 4,001 feet. The unit is narrow — varying from about 1.5 miles wide near Crook to nearly 3 miles wide near Iliff — and follows the South Platte River corridor through a series of braided channels, sandbars, and timbered river islands. Surrounding terrain is level to gently rolling agricultural land with limited topographic relief. Total unit area is approximately 77 square miles (49,059 acres).

The majority of GMU 91 is private land (approximately 79% private, 21% public/state by area). There is no National Forest or BLM land in the unit. Public access is provided by three parcels: (1) Tamarack Ranch SWA — 10,695 acres spanning GMUs 91 and 93; mandatory check-in/check-out at the check station required; hunters must park at the area checked into; on opening weekend of regular plains rifle deer season and first day/weekend of late plains rifle deer season, only deer hunting is permitted; hours 4 a.m.–9 p.m.; (2) Bravo SWA — 1,082 acres in GMU 91 (coordinates 40.6597, -103.1417, Logan County); hours 4 a.m.–9 p.m.; recreational activities except deer hunting prohibited on opening weekend of regular plains rifle deer season and opening day/first weekend of late plains rifle deer season; valid hunting/fishing license or SWA pass required for visitors 16+; (3) Ford Bridge State Trust Land — 280 acres in GMU 91; accessed 7.5 miles northeast of Sterling on US 138 to CR 40, then east 0.5 miles; centerfire rifle hunting prohibited; open September 1 through end of February, 4 a.m.–9 p.m.; valid hunting/fishing license required for visitors 16+. Unit boundaries: north — US Highway 138; east — Red Lion Road (Logan County Road 93); south — I-76 and US 6; west — US Highway 138. Sterling (Logan County seat) is the nearest town with full services.

Three habitat types dominate: irrigated cropland (approximately 65% of the unit), sandsage/mid-grass prairie (approximately 20%), and cottonwood riparian corridor (approximately 10%). The riparian corridor along the South Platte supports Russian olive, cottonwood, willow, cattails, and marsh grass. Adjacent private land is planted primarily in corn, hay, and alfalfa. Conservation Reserve Program (CRP) grasslands contribute additional cover in the broader region. There is no spruce-fir, aspen, pinyon-juniper, or alpine habitat; the unit is fully plains-grassland and agricultural in character.

Both mule deer and white-tailed deer inhabit the unit; mule deer are found across all habitat types with highest densities in sandsage rangeland and irrigated cropland, while white-tailed deer concentrate in the cottonwood riparian corridor along the South Platte. Prior to 1960 the eastern plains were almost exclusively mule deer range; whitetail populations have expanded significantly since. CPW estimates 60–65% of the D-44 (South Platte River) deer herd resides in GMUs 91, 92, and 96. Chronic wasting disease (CWD) is well established in this area; specific prevalence percentages from 2019 mandatory testing (cited in some sources as approximately 25.6% in mule deer bucks, 12.2% in mule deer does, and 15.9% in whitetail) could not be independently verified against current CPW maps and should be confirmed via CPW's current CWD prevalence maps. Pronghorn are present in open sandsage and grassland habitat; the pronghorn rut runs early September through mid-October. Elk are described as nearly nonexistent in this unit. Wild turkey, pheasant, dove, quail, and waterfowl are also present at the state wildlife areas. Deer movement correlates with the agricultural cycle — deer concentrate in corn and alfalfa fields, with the rut beginning as early as late October and running through late December.