The Fontenelle Dam is located on the Green River 24 miles southeast of La Barge, Wyoming. A zoned earthfill structure, the dam is 139 feet high with a crest length of 5,421 feet, and a volume of 5,265,000 cubic yards of material. The spillway consists of an uncontrolled crest, open chute, and stilling basin with a design capacity of 20,200 cubic feet per second. Fontenelle Powerplant is located adjacent to the toe of the dam, with the power penstock branching from the river outlet works. The powerplant consists of one 10,000-kilowatt generator and one 16,000-horsepower hydraulic turbine.
The reservoir has an active capacity of 150,500 acre-feet and a total capacity of 345,360 acre-feet, with a surface area of 8,058 acres. The lake is 20 miles in length when full, and has a shoreline of approximately 56 miles.
Conditions at the Fontenelle Damsite were found to be suitable for the dam as planned. The damsite is in a wide-bottomed valley, which slopes up steeply in nearly vertical cliffs on the right or west abutment and slopes up gently on the left or east side. Bedrock is exposed on the entire right abutment from the river level to about elevation 6,530 feet. Rock is exposed on much of the left abutment, especially in the small gullies, which cut the face of the slope. Bedrock at the damsite belongs to the upper part of the Green River formation and is composed of thin-bedded, well-consolidated shale, siltstone, and thin beds of sandstone. The bedrock lies horizontally and is cut by numerous contraction joints and settlement cracks near the surface and in the steep right abutment.