The former 8.75-acre Washougal Gap Filler Annex is currently known as Larch Mountain Radio Site, operated by the DNR as an unmanned radio repeater station. The facility is located on Larch Mountain, 20 miles east of Vancouver, and north of Washougal. It was developed between 1959-61 and used as an unmanned radar station, which included an access road, a 21` X 41 concrete block building, 4,000-gallon above-ground fuel storage tank, radar tower, primary distribution line, sanitary latrine, sidewalk, storm drainage and security fence.

The site was used by the Air Force between 1961 and April 15 1964, when it was declared excess, and the joint use leases terminated in December, when the property reverted back to DNR.

The current Larch Mountain Radio Site was constructed by DNR in 1983. All remaining DOD structures were removed at that time, including the 4,000-gallon fuel tank. New structures include a new underground diesel storage tank, 25` X 50` concrete building, 6` X 8` concrete pad, three communications towers app 60, 80, and 100 feet tall, and a barbed wire fence with 6-foot high gate.

Four sets of abandoned concrete anchor points stamped with `DNR` are located to the southwest of the facility, and a pile of discarded, broken-up concrete is located to the south of the current facility.