The California Division of Safety of Dams engineers inspect over 1,200 dams annually to assure they are performing and being maintained in a safe manner. In addition, the Division periodically reviews dam stability and stability of major appurtenances in light of emerging design approaches (earthquake hazards, hydrologic estimates) and construction requirements. Even with seismic activity, dam failures are rarely catastrophic events. Dam failures typically begin to indicate signs of wear or weakness through seepage noted in the downstream face or near the toe.
The City of Portola lies approximately 8 miles downstream of Lake Davis, which is the reservoir created by the Grizzly Valley Dam. The Grizzly Valley Dam was completed in 1915, is within the jurisdiction of the State of California, and is owned and operated by a federal agency. Government Code, Section 8589.5, requires dam owners to prepare and submit copies of inundation maps in the event of a dam failure. Inundation maps are available to appropriate public safety agencies and cities that can be affected. All Dam owners must also have an emergency action plan if a potentially unsafe condition develops.