Mossyrock Dam

• Year completed - 1968
• River system - Cowlitz
• Original investment - $117.8 million
• Type of dam - concrete arch /gravity and embankment
• Height - above riverbed, 365 feet; above bedrock, 605 feet
• Length - 1,648 feet
• Width - top 27 feet, base 115 feet
• Volume of concrete in dam - 1.27 million cubic yards
• Average flow - 5,140 cubic feet/second
• Drainage area - 1,042 square miles
• Reservoir length - 23.5 miles
• Miles of shoreline - 52 miles
• Reservoir area at maximum elevation - 11,830 acres
• Reservoir elevation - full, 778.5 feet; lowest allowable, 60 feet
• Average annual generation - 1,100,000,000 kilowatt-hours
• Equivalent number of NW homes served - 78,500
• Number of generators - Two 150,000 kilowatt generators 
• Installed capacity (nameplate rating) - 300,000 kilowatts

Mayfield Dam

• Year completed - 1963
• River system - Cowlitz
• Original investment - $44.5 million
• Type of dam - concrete arch/gravity and embankment
• Height - above riverbed, 200 feet; above bedrock, 250 feet
• Length - 850 feet
• Width - top, 5 feet; base, 23 feet
• Volume of concrete in dam - 110,000 cubic yards
• Average flow - 6,120 cubic feet/second
• Drainage area - 1,400 square miles
• Reservoir length - 13 miles
• Miles of shoreline - 33.5 miles
• Reservoir area at maximum elevation - 2,250 acres
• Reservoir elevation - full, 425 feet; lowest allowable, 415 feet
• Average annual generation - 804 million kilowatt-hours
• Equivalent number of NW homes served - 57,500
• Number of generators - Four 40,500 kilowatt generators 
• Installed capacity (nameplate rating) - 162,000 kilowatts