FORT COLLINS, Colo. — Severe flooding in the Four Corners region Friday led to water rescues — some from rooftops — and impassable roads, with some residents urged to evacuate low-lying areas of Colorado and New Mexico and others to stay where they are until levels go down.

The flooding was caused by heavy rain in the desert where Arizona, Colorado, New Mexico and Utah meet, with more rain in the forecast through at least Saturday. Hundreds of people along the San Juan River in the biggest city in the area, Farmington, New Mexico, were told to evacuate.

Downstream, residents of the vast Navajo Nation braced for floodwaters not expected to peak until late Friday or early Saturday.

“Do not wait to make your evacuations.…