
The cantonment area seen in this photo is no longer extant, as shown in the 'Inset' (upper left). Source: http://home.nps.gov/chis/photosmultimedia/santa-rosa-island-photo-gallery.htm

1977 view of the cantonment area from the harbor
Photo source: http://www.radonboats.com/newsletter23.html

source: http://www.davestravelcorner.com/photos/unitedstates/california/central/index.htm
Based upon the elevation, the ground cover, and the trees seen, this very likely was the former radar site / technical operations area on Santa Rosa Island, CA. The ground appears to have been "restored."
If the view is to the northeast, looking from a point near the southwest end of the former site, the trees would match precisely to what is seen in the "Google Earth" aerial image. Also, what looks like a road is seen to the far right, and -- if the view indeed is to the northeast -- then that is precisely where the site access road would be seen.

Radar site - NPS photo

Cantonment area - NPS photo (1965)