On April 22, 2001, at 1130 hours Pacific daylight time, a Ryan ST3KR, N46503, was substantially damaged when the aircraft's wing impacted a post during taxi for takeoff at the French Valley Airport, Murrieta, California. The airline transport certificated pilot and one passenger were not injured, and intended to conduct a local area flight. Visual meteorological conditions prevailed and no flight plan was filed for the personal flight, which was operated by the owner under 14 CFR Part 91. The pilot reported that, as he taxiied the tailwheel equipped aircraft into the run-up area adjacent to runway 18, the underside of the left wing struck a 4-foot-tall pole protecting a fire hydrant. The pilot was seated in the rear cockpit of the tandem-seating aircraft. He reported that the presence of another aircraft entering the run-up area at the same time made it necessary to alter his taxi route and, after he turned sharply, the low post was too close to be visible from the rear cockpit. The pilot also noted that the hydrant was one of two positioned within the operational area of run-up pad and there were no hazard markings painted on the asphalt around the hydrant.