The 2770-acre Leslie Canyon area was established in 1988 to protect habitat for the endangered Yaqui chub (Gila purpurea) and Yaqui topminnow (Poeciliopsis occidentalis sonorensis). The refuge also protects a rare velvet ash-cottonwood-black willow gallery forest. This area is part of the basin and range geologic region, characterized by linear mountain ranges which are separated by broad, flat basins. The region was impacted by relatively recent volcanic activity, leaving volcanic plugs and cinder cones visible throughout the San Bernardino Valley. Earthquakes have further altered the region and helped allow the flow of many springs and seeps. All of these dynamic geological events have played major roles in shaping the valley, catching and storing crucial water, helping determine the variety of plants and animals present, and creating a beautiful landscape for humans to enjoy.