A number of Pomo were enslaved and abused by settlers, including Andrew Kelsey, whose name is attached to the town of Kelseyville today, and Charles Stone. The Pomo finally revolted and killed Kelsey and Stone. A United States Army contingent under Lieutenant Nathaniel Lyon cornered as many as 200 Pomo on an island in Clear Lake, and slaughtered most of them—including scores of women and children. The historical marker for Bloody Island is on Highway 20 between Upper Lake and the Robinson Rancheria. Later, the Pomo were forced to live in small "rancherias" set aside by the federal government. For most of the 20th century, the few remaining Pomo people had to live on these tiny reservations in poverty. Today the fastest-growing businesses around Lake County are the casinos presently operated by four Pomo rancherias, with more casinos planned. Clear Lake was used as an outlying seaplane base for Alameda Naval Air Station during World War II and the early years of the cold war. Flying boats could land on Clear Lake when landing conditions were unsafe on San Francisco Bay. Exhibits and programs about the region's culture and history are maintained and presented by rangers and docents at Clear Lake State Park and at Anderson Marsh State Historic Park. Lake County has two county museums, the Lake County Museum in Lakeport and the Lower Lake Historical Schoolhouse Museum in Lower Lake. There are also numerous state and local historical landmarks identified throughout the county. Hydrology and water rights The Clear Lake Watershed is contained within the Upper Cache Creek USGS hydrologic unit, an area that encompasses . The drainage basin is ( including the lake), which is large compared to the lake's . The surface area of the lake is divided into three arms: the Upper Arm, the Oaks Arm and the Lower Arm. Cache Creek, the only outlet for the lake, originates from the Lower Arm. Cache Creek has two major tributaries: North Fork Cache Creek and Bear Creek. The Upper Arm is the largest of the three arms and receives 75% of drainage from the watershed. Rodman Slough, contained within the Upper Arm, receives drainage to its marsh from Scotts Creek and Middle Creek, the largest tributaries to Clear Lake as well as Kelsey Creek, which enters from Big Valley. Erosion and sedimentation are key environmental concerns in the Clear Lake region. Seventy percent of the terrain