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The California Department of Water Resources estimated, on a preliminary basis, in its "Preview of Bulletin No. 136, North Coastal Area Investigation--September 1963," that 1,200,000 acre-feet of yield could be developed from Helena and Eltapom Reservoirs, together with the associated diversion and power facilities at a total cost of $540,000,000. Helena Dam would be an earth, gravel, and rockfill dam about 560 feet high. The dam would be located about three miles downstream from the community of Helena. A reservoir of 2,800,000 acre-feet would be created with a normal water surface elevation of 1840. This would back water up to the toe of existing Lewiston Dam of the Trinity River Division, Central Valley Project. The aforementioned State report indicates that Helena Dam would develop an average annual yield of 600,000 acre-feet, primarily from the watershed below Lewiston Dam. The second major storage facility would be Eltapom Dam and Reservoir. As tentatively planned, Eltapom Dam would be an earth and rockfill structure about 650 feet high located about one mile downstream from Hyampom Valley. It would provide a gross storage capacity of 3,100,000 acre-feet with a normal water surface elevation of 1840. A minimum operating water surface elevation of 1670 would provide an active storage of about 1,550,000 acre-feet and an average annual yield of about 600,000 acre-feet, according to estimates given in the State report. Complex geological problems at the damsite will require extensive exploration, study, and analysis before designs can be finalized. Water released from storage in Eltapom Reservoir would be diverted by gravity to Helena Reservoir through the Eltapom-Helena Tunnel. This tunnel would be about 13 miles long, 20 feet in diameter, and would have a capacity of 1,730 c.f.s. It would be sized to allow for future additional diversions from the Mad and Van Duzen River systems. Water from Helena Reservoir would be diverted to Clear Creek (tributary to Sacramento River) by means of the Helena-Towerhouse Tunnel. This tunnel would be 12.8 miles long, just under 21 feet in diameter, and have a capacity of about 3,990 c.f.s. This tunnel also would be sized to allow for the conveyance of future flows from the potential Mad-Van Duzen River development. Flows from the Helena-Towerhouse Tunnel would discharge directly into Towerhouse Reservoir which would be located on Clear Creek just above the existing Whiskeytown Reservoir of the Trinity River Division, Central Valley Project. Towerhouse Dam would be an earth and rockfill structure about 300 feet high and would provide maximum 7Epson Perfection 4870 Photo, 400 dpi, 8 bit, 13,438,976 byte