The lookout structure, a California Region 5 Plan BC-301 on a 10 foot open timber tower was built in 1935. The lookout replaced an earlier guard station building that had been built for double duty as a lookout site in 1932.

Reservoir Summit was located west of the Old Ridge Route, and east of the current Interstate 5 and Pyramid Lake in Los Angeles County. 

Reservoir Summit was abandon by 1947 due to increasing smog. The lookout's removal date is unknown.

Jack Rimmer's words in "Ridge Route -  The Road That United California" by Harrison Irving Scott are paraphrased by John Damann:

"Reservoir Summit, elevation 3,883 feet. There was a cafe, garage and a service station.They were located on the east side of the road.The restaurant had a fabulous view literally hanging over the cliff. On the west side of the road directly west of the former cafe is the large cement -lined water reservoir.In 1931/32 it also had a Ranger Station on Reservoir Hill and in 1932 a new fire truck was assigned to the Ridge Route to be stationed at Reservoir Summit Guard Station.

The new engine was painted red, as all other F.S. equipment was green. The only structure was an old ship-lath combination mess hall/bunkhouse. The F.S. was in the process of building a new garage for the new fire engine,and a new combination home and lookout station for the ranger.The station had two magneto crank telephones,one connected to the F.S. line and other to Pacific bell.They would take Azimuth Readings from the porch and report the degree to the Newhall Ranger Station.

Most forest stations were guard stations. At Reservoir Summit, the crew of eight including the cook were stationed there, they functioned similar to the CCC camp.They had a new fire truck with crew,and a pick'up type patrol vehicle that carried approx.two to three hundred gallons of water for fire control, with fire equipment. In completing the finishing touch of the new house and garage. The crew treated the wooden flooring with linseed oil. Unfortunately they left the oily rags on the floor and that lead to spontaneous combustion, and burned down the whole station that was never rebuilt. In 1935 it was then replaced with the Summit Reservoir Lookout tower."

Thanks to Mike Guerin for the information and images.