On August 11, 1995, at 1445 hours mountain daylight time, a Mooney M20A, N8378E, was substantially damaged during a loss of control on takeoff following an encounter with uneven terrain at the Rock Springs Municipal Airport, Rock Springs, Wyoming. The private pilot and passenger were uninjured. The business flight was to have been operated under 14CFR91, and was destined for Gillette, Wyoming. Visual meteorological conditions prevailed and no flight plan had been filed. Intersecting runways 09/27 and 03/21 were closed (NOTAM issued) at Rock Springs due to construction and the airport had received authorization to conduct takeoff/landing operations from the parallel taxiway for runway 09/27. The authorization was provided by the FAA's project manager for the Rock Springs airport, an engineer attached to the FAA's Denver Airports District Office. The pilot reported that he commenced his takeoff roll from taxiway A-2 (refer to attached diagram) and that, upon passing into the crossing intersection of taxiway A-3 the aircraft encountered a "crown" in the temporary runway surface at 65 to 70 knots airspeed. The airplane was launched into the air without enough speed to remain airborne. The pilot stated that the airplane hit the ground and bounced back up into the air, off the north side of the temporary runway. During the second ground impact the aircraft struck an informational sign and then skidded to rest between the temporary and permanent runways 09/27. No information was made available to pilots by the airport regarding the crowned condition of taxiway A-3 during takeoffs/ landings. No FAA airports personnel inspected the temporary runway where it crosses taxiway A-3 noting the crowned condition.