The victim, who was not identified, told Missoula County sheriff's deputies that after hearing something behind her that sounded as loud as a car, she turned but was unable to avoid the careening mountain bike, which ran up her back, according to Lt. Rich Maricelli.

A witness who narrowly avoided the bicyclist about 100 yards up the trail estimated the red bike was traveling 30 mph to 35 mph, he said.

The collision knocked both the hiker and bike rider to the ground, but the cyclist jumped up, got back on his bike and continued down the hill.

"He didn't say a word," said Maricelli.

Once at the trailhead parking area, the bicyclist and a fellow rider, who wasn't traveling as fast, threw their bikes into the back of a black Nissan truck and left the area, he said.

Authorities don't know which direction the truck traveled after turning off Road No. 365 onto Blue Mountain Road.

"The problem was that he left the scene," said Maricelli.

If located, the bicyclist could be charged with reckless endangerment, similar to a motorist involved in a hit-and-run.

The victim required stitches but was treated at Community Medical Center and released.

Maricelli said warmer temperatures mean more people are outside and on area trails, and he reminded recreationalists to watch out for others.

Anyone with information about the incident is asked to call Crimestoppers at 721-4444.