This symbol is on the tarmac at Ramona, CA airport. I've seen it at other small GA airports from Google Earth but I don't know what it is. Can someone please explain?
That is a Compass Rose, painted on a Compass Calibration Pad. It's used to mark a location on the airport surface that is suitable for calibrating the compass of an aircraft.
More information on the requirements for the compass rose / compass pad can be found in AC 150/5300-13, in Appendix 6.