In 1971, wild horses and burros were found roaming across 53.8 million acres of Herd Areas (HAs), of which 42.4 million acres were under the BLM's jurisdiction. Today the BLM manages wild horses and burros in subsets of these HAs, known as Herd Management Areas (HMAs) that comprise 31.6 millionacres, of which 26.9 million acres are under BLM management.
Location: The Cibola-Trigo HMA extends north from Imperial Dam and to the west of the Colorado River to Walter Camp, Calif. The HMA is primarily between U.S. Highway 95 and the Colorado River, and Interstates 8 and 10. The southern boundary of the HMA is about 20 miles north of Yuma, Arizona. Size: The HMA comprises nearly 1 million acres in the lower Sonoran Desert. Habitat: In Arizona, the Cibola-Trigo HMA supports both wild burros and horses. In southeastern California, only burros roam between the river and the Chocolate/Mules and Picacho HMAs.
Winters in the HMA are typically mild, but summers can be dangerous, with temperatures exceeding 125 degrees. Wild burros share this habitat with desert bighorn sheep and desert mule deer. Other animals living in the HMA are desert tortoises, rattlesnakes, and a variety of birds and lizards. History: Wild burros were likely introduced into this area in the mid-1800s. As mining booms went bust and alternate transportation became available, the wild burros were left to fend for themselves. Wild horses have a more recent history. These animals probably escaped or were released from ranches when the river was channeled in the 1940s. There are several Appaloosa studs thriving in the Arizona portion of the HMA, contributing to the color diversity of the herd. In fact, this line may be a continuation from the first-ever Appaloosa stud in the area.
Burros evolved in the harsh deserts of North Africa and are well adapted to the dry desert environment. Left alone in this remote region with few natural predators, the wild burro population flourished. Today, the burro population in the HMA is about 500. The burros found here are typically gray and are fine boned. They average about 400 pounds and 40 inches in height. During the summer months, the burros congregate along the Colorado River or other water sources. In late fall and early winter, depending upon rainfall, the burros disperse across the HMA. They begin their move back to the river in May or early June when temperatures rise and the mesquite beans ripen. The wild horses remain near a permanent water source year round. There are about 240 wild horses within the HMA.