Officials issued a warning about the risk of the Mojave River Dam's failing. The U.S. Army Corps of Engineers has elevated the risk from low to "high urgency of action."
A recent assessment found that during an extreme flood event, water could exceed the capacity of the dam and overtop it.
This could potentially result in dam failure, flooding Hesperia, Apple Valley, Victorville and Barstow. Flood waters also could reach Baker, more than 140 miles downstream of the dam.
The agency is looking at risk-reduction measures and anticipates some will be in place before this year's winter rains.
Built in 1971, the Mojave River Dam was designed and constructed consistent with the standards of the day. It continues to operate as it was designed and reduces risk for more than 16,000 people and $1.5 billion in property.
Mojave River Dam: 'Extreme' flooding event could put Californians at risk, officials say