(CNN) Hundreds of thousands of people live downriver from a dam in California that recently had its risk characterization changed "from low to high urgency of action" by the US Army Corps of Engineers.

Those communities, which include Hesperia, Barstow, Apple Valley and Victorville, could flood if the Mojave River Dam fails, a statement from the agency said.

More than 315,000 residents in those four communities in San Bernardino County, about 70 miles northeast of Los Angeles, are in the path should floodwaters overtake the dam, according to US Census data.

The Mojave River Dam is an ungated flood control structure built in 1971 that is located at the northern side of the San Bernardino Mountains.

Southwest of the dam, on the other side of the mountains, residents are fleeing wildfires in the region. The dam is located on the "desert" side of the mountains, so the current wildfires don't add any risk to the flood threat, CNN meteorologist Haley Brink said.

Read More