By Electa Draper Denver Post Staff Writer “Once a track is exposed, it’s like a ticking clock,” says Andre Delgalvis, a Grand Junction resident who has made some rare fossil finds on Lake Powell’s temporarily exposed shore. Bullfrog, Utah - Andre Delgalvis scrambles over new shoreline at Lake Powell and spies three-toed dinosaur tracks only recently exposed by plunging water levels at the desert reservoir.