has very shallow top soil, which saturates after a rainfall of , after which runoff flows quickly into the lake. The maximum flow from the lake is determined by the narrow canyon of Cache Creek, not by the dam. The combination of rapid inflow and slow outflow results in frequent flooding of low elevation areas such as downtown Clearlake and Lakeport. DeWitt Clinton Rumsey, previously a cattle drive "Captain" (and after whom the town of Rumsey in Yolo County was named), was one of the first to record the water levels of Clear Lake. Its level was originally controlled by a rocky ledge in Cache Creek, called the "Grigsby Riffle" (which is now submerged upstream of the 1914 dam). In 1872 Rumsey installed a gauge in Lakeport to record the water level. He defined the level when the lake ceased to flow over the ledge as "Zero feet Rumsey", which corresponds to an elevation of . The reading is called "on the Rumsey Gauge" or "Feet Rumsey", which can fall below zero due to evaporation (over a year) and pumping of water. The highest recorded level is ( in 1890, and the lowest is in 1920. In 1991 a court ruled that the official "low water mark" (which determines property ownership) is Zero feet Rumsey. The Rumsey gauge, now automated, is still in operation. Yolo County acquired riparian rights to Cache Creek's water in 1855, and after gaining water storage rights in 1912 they built the Cache Creek dam. Water companies which rely on the lake have to pay Yolo county for their water. The Gopcevic (1920) and Bemmerly (1942) Decrees prohibited the modification of the Grigsby Riffle, set the normal maximum level of Rumsey, and required Yolo to keep the level below except for limited times during floods. Yolo was entitled to use all the water down to zero feet. The Solano Decree (1978,1995) limited the amount of water Yolo could use: if the lake is "full" on May 1—at Rumsey—then they can draw 150,000 acre-feet, equivalent to a drop in the lake level of about . If the level on May 1 is below they can draw none, with a proportional amount for other levels. They must stop on October 31, or if the level falls to . In compensation the Indian Valley Reservoir, also entirely in Lake County, was constructed in 1975, and is under the full