Unit 36A, Arizona

Elevation ranges from approximately 2,500 feet in the desert valleys near Three Points and the Altar Valley floor to 6,188 feet at Keystone Peak in the Sierrita Mountains — the unit's highest point. The Sierrita Mountains form the dominant highland feature; the Cerro Colorado Mountains (highpoint ~5,319 ft at Colorado Peak) are the most rugged sub-range, and the Las Guijas Mountains (highpoint ~4,665 ft, lying northwest of Arivaca) occupy the southwestern portion. Terrain transitions from relatively flat desert grassland and rolling mesquite washes at low elevations to moderately steep to extremely steep rocky slopes and canyons in the mountain ranges. The unit is separated from the Santa Rita Mountains to the east by the Santa Cruz Valley.

Primary vehicle access enters from AZ Hwy 86 (Ajo Way) at Three Points, then south on AZ Hwy 286 approximately 38 miles to Buenos Aires NWR headquarters (about 7.5 miles north of Sasabe); alternatively via I-19 Amado/Arivaca exit west on Arivaca Road ~35 miles to AZ Hwy 286. The unit boundary is defined by AZ Hwy 86, AZ Hwy 286, the Arivaca–Sasabe Road, Arivaca Road, I-19, and Sandario Road. Public land comprises roughly 72% of the unit: state trust land (largest portion), Buenos Aires National Wildlife Refuge (~117,107 acres managed by USFWS), and limited BLM parcels. Hunting is permitted on approximately 90% of the refuge; the Buenos Aires NWR has 83 primitive dispersed campsites (no fee, first-come) and Pronghorn Drive, a 10-mile loop through refuge grasslands (high-clearance recommended). Road access is generally good but some roads require 4WD or high-clearance vehicles. Key private ranches in 36A — including Diamond Bell Ranch, Marley Ranch, and Rancho Seco — are Pima County properties opened to hunting under Note 129 of the Commission Order. Mining activity in the eastern portion (Sierrita Mine area) restricts access near active operations. Approximately 3,500 acres along the U.S.–Mexico border within Buenos Aires NWR were closed to public access due to border-safety concerns. Brown Canyon on the refuge's western edge (Baboquivari foothills) is closed to general public access. There is no designated wilderness in 36A. Nearest services: Tucson (40+ miles northeast), Green Valley, Amado, Arivaca, and Three Points/Robles Junction.

Low elevations (below ~4,000 ft) support upper Sonoran Desert grassland, Sonoran Desert scrub, saguaro cactus, mesquite, and creosote typical of the Altar Valley floor and rolling foothills. The intermediate zone features ocotillo, prickly pear, sotol, and mixed desert shrub. Higher elevations in the Sierrita Mountains transition to oak woodland, chaparral, and manzanita; the highest ridges support juniper and scattered oak. Riparian corridors along Arivaca Creek support sycamore, cottonwood, and willow — including the Arivaca Cienega wetland and Arivaca Lake, rare semi-desert grassland wetlands within Buenos Aires NWR. The refuge protects an extensive block of semidesert grassland in the Altar Valley maintained by prescribed and natural fire.

Coues white-tailed deer inhabit all mountain ranges, foothills, and oak-chaparral zones at mid and upper elevations, with lower-density populations moving into valley flats and mesquite washes. Desert mule deer occur in the lower foothills, rolling grassland washes, and desert scrub; range overlap with Coues deer is notable in the Sierrita foothills. Javelina are widespread throughout the unit from desert scrub to oak woodland. Black bear range through the Sierrita Mountains and are present under Zone P OTC nonpermit-tag management. Mountain lion inhabit the mountain ranges (Zone P, units 29–36C combined). Pronghorn are present on Buenos Aires NWR, where reintroduction of masked bobwhite quail and grassland species has been a primary management focus; current pronghorn density in the broader unit is low. The refuge supports 58 mammal species total including occasional vagrant jaguar from Mexico. Gambel's, scaled, and Mearns' quail are all present; hunters must be able to identify protected masked bobwhite quail that may occur outside refuge boundaries in 36A and neighboring units. Feral hogs have been documented on the refuge. Coues deer rut peaks mid-to-late December.