Historic California Post Camp Stations and Airfields
Hayfork Gap Filler Annex SM-157C
Typical AN/FPS-14 Gap Filler Radar
"During the late 1950s another area of progress was the development and deployment of AN/FPS-14 and AN/FPS-18 gap-filler radars. Having a range of around sixty-five miles, these radars were placed in areas where it was thought enemy aircraft could fly low to avoid detection by the longer-range radars of the permanent and mobile radar networks. Gap-filler radar deployment peaked in December 1960 at 131 sites throughout the continental United States. Because the introduction of gap-filler radars alleviated the need for civilians to scan the skies for enemy bombers, the ADC disestablished the Ground Observer Corps on January 31, 1959."
Searching The Skies
USAF Air Combat Command
June, 1997
Typical floorplan of a Gap Filler Annex
SITE NAME(S): Hayfork Gap Filler Annex. The site was also known as Hayfork Gap Filler Annex (SM-157C) Military Reservation.
LOCATION: The site is located in Trinity County, California and is situated approximately six miles north of Hayfork on top of Hayfork Bally.
SITE HISTORY: In 1958, the U.S. Government acquired 0.23 permit acre from the Department of Agriculture, U.S. Forest Service (USFS). It was used as an unmanned gap filler radar station by the U.S. Air Force. The improvements were one concrete block building for equipment and generator, two 15,000 gallon underground fuel storage tanks, a steel antenna tower, a woven wire fence, and a gravel surfaced road. In 1963, the 0.23 permit acre was retransferred to USFS. The site is currently being used by Trinity County as an unmanned communications station and by USFS as a fire watch station.
The site was the third of three unmanned radar stations that provided coverage for those areas not covered by the radar located at Red Bluff Air Force Station. The other two were located at Janesville (Site SM-157A) and Whitmore (Site SM-157B)
Source: Sacramento District, US Army Corps of Engineers
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Updated 8 February 2016