A fire that broke out today in the Santa Ana River bottom between Jurupa Valley and Riverside scorched three acres in less than an hour and burned toward structures as crews attempted to encircle it.

The non-injury blaze was reported at 11:10 a.m. in the area of Jurupa Avenue and Van Buren Boulevard, less than a mile north of Riverside Municipal Airport, according to the Riverside County Fire Department.

Multiple engine and hand crews from the county and city of Riverside converged on the location and encountered flames moving at a moderate rate eastward through thick vegetation.

Two Cal Fire water-dropping helicopters were sent to make runs on the fire, which was moving toward businesses abutting the river bottom in Riverside, according to reports from the scene.

No evacuation orders were imminent.

There was no word on what might have triggered the fire. The river bottom is dotted with homeless encampments, and during dry periods, fires from camping and cooking are a regular occurrence.

More than 1,500 fires were reported by the start of May in California, where firefighters are bracing for a hot and dry summer following another winter of below-average rainfall.

CAL FIRE reported 1,575 wildfires through May that burned 3,531 acres. At the same time last year, the agency reported 938 fires that burned 1,166 acres.

California’s five-year average for the same period is 766 fires and 2,870 acres.