How can I find the location and coverage of aviation VHF transmitters? In the USA, is there a way to find locations of VHF transmitters that are used for air traffic communication, and the frequencies they transmit/receive on? There are some places (Northern Bay Area, CA) where I fly where I have good signal/communication with a Terminal Radar facility, but have trouble contacting area approach in the same area - especially when low (&lt;2000ft AGL). The area is hilly.

I'm interesting in seeing range and altitude support for a given frequency (in a given area).
This is a useful site for the Oakland (ZOA) Air Route Traffic Control Center (ARTCC), and the locations of these match up with the RCO locations on the sectional. It seems Mt Tamalpais RCAG is the one that applies to my area. The list seems a little out of date, however, as the location of "Priest - RCAG" doesn't have anything on the sectional, or in Google Maps.

Further, there is an FAA site depicting RCOs and frequencies for Alaska.