Unit 66A, Idaho

Mountainous terrain ranging from approximately 5,700 feet at valley bottoms to roughly 8,900 feet on high peaks, with Caribou Mountain rising above the surrounding marshes. The unit is 171,578 acres (about 268 square miles) and features steep forested drainages, high meadows, and the marshy, flat floodplain of Grays Lake National Wildlife Refuge at the western edge. The Motorized Hunting Rule applies, restricting vehicle use to established roadways open to full-size automobiles from August 30 through December 31.

Access is primarily via State Highway 34, which forms the southern boundary and connects to Soda Springs and the broader region. Key entry roads include McCoy Creek Road (Forest Service Road 087), which runs along the northern boundary from the Wyoming state line west through the community of Herman; the Bone Road, which follows the western boundary south from Herman to Hwy 34; and the Grays Lake Road (West Side Road), which provides access to the western portions along the wildlife refuge edge. All lands within unit boundaries are administered primarily by the Caribou-Targhee National Forest (65.71% USFS per IDFG), with private land at 17.69%, State of Idaho at 1.73%, BLM at 0.54%, and the remainder split among other federal entities. There are no federally designated wilderness areas within GMU 66A. Interior trails are closed to motorized vehicles; ATVs and OHVs are restricted to full-size vehicle roads per the Motorized Hunting Rule. Fox Hills Ranch participates in the Idaho Access Yes! program (accessible via the Diamond Creek elk hunt area).

Dominated by forest (approximately 64% of the unit), with conifer cover including Engelmann spruce, subalpine fir, Douglas-fir, and lodgepole pine at higher elevations, and aspen groves mixed through mid-slopes. Lower-elevation transition zones feature bigtooth maple brush, chokecherry, serviceberry, and scattered juniper alongside sagebrush and grassy meadows. Riparian areas (approximately 14-15% of the unit) follow creek corridors with willows and cottonwoods. The Grays Lake basin supports extensive cattail marshes and bulrushes, providing important staging habitat for sandhill cranes and waterfowl. Approximately 8% is open rangeland/sagebrush-steppe on lower benches.

Rocky Mountain elk are the primary draw and are present in good numbers; the 2023 Diamond Creek Zone population survey showed estimates within management objectives. Elk summer in the high country and move to lower drainages and the sagebrush/aspen transition as winter approaches. Mule deer are present unit-wide; populations were significantly reduced after the severe 2022-23 winter but have been recovering, with 2025 harvest (58 deer, 18% success) up from 2024 (34 deer, 10% success). Both Shiras moose and black bear inhabit the unit, with moose frequently associated with riparian and marshy areas near Grays Lake. Mountain lion are resident, and gray wolf packs are documented in the area. Grays Lake National Wildlife Refuge, which abuts the western edge of the unit, is one of the world's largest nesting areas for greater sandhill cranes and supports large numbers of waterfowl.