Lompoc Firefighters responded to reports of a fire just north of the Robinson Bridge at approximately 6:45 p.m. Wednesday.
When units arrived they say they saw a large plume of black smoke coming from the riverbed that is a known location of a large homeless encampment.
Officials say there were several propane gas tanks involved in the fire.
Crews were able to contain the fire after about 20 minutes, and remained on scene for two hours mopping up hot spots.
There were no injuries reported, and the cause of the fire remains unknown.
Officials say this was the second fire in the last three days located in the same area.