eight miles north of powell, wy. driving in my pickup on a narrow, paved,steep road enroute to the powell airport so i could fly my airplane to greybull, wy, for dynamic propeller balancing. time 0730 mdt; date 13 july 2000; ceiling and visibility unlimited; wind calm; crystal clear with no smoke or haze. sighted a perfect ellipticlly shaped object to the north, (azimuth approx 350) elevation angle approx 30 deg. major axis parallel to a horizon. length of object subtended 1 and 3/4 inches at a "short" arm's length. length along the major axis about three times that along the minor axis. object appeared stationary. i did not stop as no real shoulders and a steep dropoff to the left (south), although i would have stopped were i to have had a camera. color of object kind of a flat silvery, grayish white, somewhat similar to the light areas of a daytime moon; no color gradations; no markings; no lines; no shadows. i don't know if it were a small object nearby or a large object far away. would lean towards the latter. I couldn't tell if it were a true ellipse in shape or a circular object at a tilt. object was in sight for approx 35-40 seconds. rising ground between me and the object as i neared the end of the climb caused loss of sighting. when clear after a few seconds, the object was not in sight. description of the sighting was related to my wife. about 5 other pilot friends and to the airport's fbo. coodinates of sighting (obtained from a standard aeronautical sectional chart). lat 44-52 n; 108-46 w. (deg and min). my initial thought was of a blimp; however, this was discarded after 1/100 sec as there were no tail feathers, no gondola, no engines. no color variations. no markings. i have no idea what this thing was, but it was like nothing i've ever seen, before or after, including many years as an active pilot.