Ever wonder why you see plows when there's no snow?

BOISE, Idaho (KBOI) --- If you've ever driven on one of Idaho's many mountain highways and seen a snow plow operating when there's no snow on the road, there's a reason for that.

The drivers aren't out looking for snow. They're looking for rocks.

Crews may still encounter snow at this time of year on some routes, and have the plow blade in place to deal with that if it happens. But the chief benefit of the plow is that it can be used to move rocks that are four or five feet in diameter, as well as the little ones that can take out an oil pan on a car or truck, or flatten a tire on a small car, motorcycle or bicycle.

"Some parts of our mountain roads have rocks fall on them virtually every morning and night," said Dan Bryant, southwest Idaho maintenance coordinator. "Rain, wind and temperature variations can bring them down in significant numbers."

Plow trucks are used primarily on stretches of highway with a history of rockfall, where crews are confident they will encounter rocks again. Temperatures plummet at daybreak and sunset each day in the spring, creating a volatile situation for rocks poised precariously on hillsides.