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From the Files of the Lassen Historical Society: Janesville Gap Filler Radar Site

Thursday, January 28th, 2021

The radome tower of the Janesville Gap Filler Radar Site and the Forest Service lookout on Thompson Peak in the 1960’s. photos from California State Military Museum

by Susan Couso

In a world of acronyms and technological-sounding titles, the name “Janesville Gap Filler Radar Site SM-1574” seems a little mysterious. Especially when you figure that it is a government facility. But the Janesville Gap Filler Radar Site (GFA) is exactly that… a radar site that fills a gap!

These radar installations were designed to cover the area that permanent long-range radar might miss. They had a range of about 65-miles and were considered an important safety measure to cover low-flying aircraft that was trying to avoid radar detection.

The installation of these Gap Filler Radar Sites peaked around 1960 as the ‘Cold War’ was at it’s most intense. In December of 1960, 131 sites were situated throughout the United States. This alleviated the need for civilian Ground Observer Corps members to constantly scan the sky for enemy aircraft. The Ground Observer Corps activity ended in 1959.

Work began on Janesville’s Thompson Peak Site in 1958. Just over 37 acres were acquired from the USFS, and the building construction was started near the old Thompson Peak Fire Lookout, which had been built in 1931. It became an active radar site in June of 1960.

The L-shaped building is the original building built by the Air Force. It consists of two rooms: the equipment room which once contained the transmitter and receiver, and the generator room which supplied the juice for the whole operation. It also had two 15,000 gallon fuel storage tanks, a 70-foot high steel antenna tower, a woven wire fence, and a gravel surfaced road.

Although this was an unmanned site, as gap filler annexes usually are, military personnel would have come here to perform regular maintenance and fix equipment as necessary. The property was used by the Air Defense Command as an unmanned radar gap filler station supporting the Red Bluff Air Force Station.

In March of 1969, the facility was abandoned and the property was transferred back to the USFS.

Nearby sits the old fire lookout. Due to expansive views of the surrounding area, the Civilian Conservation Corps began constructing a fire lookout and access trail in 1931. The two-story lookout was completed in 1932, and is perched on the summit. It is most recently staffed and managed by the Plumas National Forest.

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