Urban sprawl
Urban sprawl, air and water pollution, noise, light pollution, and a range of habitat restricted by human infrastructure put stress on the park's mammals and other animals, but the most serious immediate threat to them is roadkill. About 50,000 vertebrates a year die on the park's roads when they are hit by a vehicle. The Rincon Mountain District has few roads, but Picture Rocks Road, an east–west commuter highway crossing the Tucson Mountain District, is highly dangerous to wildlife. Attempts in 2002 to convert it to a hiking trail failed after the proposal met with stiff public resistance.