Rohnert Park is a city in Sonoma County, California, United States, located approximately 50mi north of San Francisco. The population at the 2010 United States Census was 40,971. It is an early planned city and is the sister city of Hashimoto in Japan. Sonoma State University, part of the California State University system, is located nearby.GeographyAccording to the United States Census Bureau, Rohnert Park has a total area of 7.0sqmi, 99.93% of it land and 0.07% of it water.HydrologyThere is a small reservoir called Roberts Lake at the north end of the city and a number of creeks. Important creeks include the Laguna de Santa Rosa (which forms part of the border with the City of Cotati), Copeland Creek, Hinebaugh Creek, Crane Creek and Five Creek.All creeks within the city limits have been channelized. Spivock Creek, Coleman Creek, Wilfred Channel, and Labath Channel are artificial channels designed to convey runoff.GeologyThe Rodgers Creek Fault is an active fault influencing earthquake activity in the Rohnert Park area. The city also experiences earthquakes from the San Andreas Fault.