The Distant Early Warning Line ("DEWline") was a system of radar stations mostly in Alaska and Canada set up to detect incoming Soviet bombers during the Cold War, and provide early warning of any sea-and-land invasion. The DEW Line was operational from 1957 to the late 1980s. Between 1988 and 1993, the stations were deactivated or upgraded as part of the new North Warning System. Click on "related web page" for a 1961 documentary about the DEW Line in Alaska and even some vintage video of Anchorage at the time.
The area was probably given away as excess federal property and claimed by Anchorage for a city park next to the Campbell Creek greenbelt. A "rocket" facility at the location has "restricted access", but the rest of the park is open to all and has more than a few forest dwelling Homo sapiens. Fortunately the cache is not in that part of the park.
The most information I could find about DEWline Rearward Communications Stations was:
REARWARD (VERTICAL) COMMUNICATIONS
The original DEWline rearward communications design used the IS-101 Ionoscatter Radio system (AN/FRC-101). This was a data-only system that could not provide voice grade circuits. Teletype channels were routed over this system to sites at Age-X (Anchorage), Nel-X (Ft Nelson BC, Canada) and Res-X (Resolution Island NWT, Canada on the east coast). Of course, the primary function was to provide surveillance data (aircraft movements) to military authority in the lower-48. This system used huge curtain antennae which were maintenance intensive. Because of the drawbacks of the IS-101 it was replaced in Alaska in the early ’60s.
You are looking for a camouflaged small-size container hidden in a spruce stand, although no spruce needles need be searched or painfully injected into your skin to get the cache.