The search for a missing 8-year-old boy with attention deficit disorder entered the fourth day Tuesday, and aircraft were expected to assist ground crews.

Evan Thompson disappeared while on a family camping trip Saturday morning outside Canon City, about 90 miles south of Denver. The area is lined by steep, limestone cliffs.

Searchers said the weather had been mild.

"There's no reason to think anything bad," said Steve Wilson, a member of the Alpine Rescue Team. "The stuff he has is probably adequate."

Crews from five counties, the military and the Civil Air Patrol were searching for the boy.