Two separate grizzly bear attacks Thursday left four people with non-life threatening injuries.
The attacks took place just west of Island Park Reservoir in Idaho and Cygnet Lakes Trail, southwest of Canyon Village trail in Yellowstone National Park in Wyoming.
In Idaho, two private contractors doing habitat assessment work were unknowingly near a bear sleeping behind a tree.
A bear charged at one of the men and bit him in the thigh and the backside, knocking him down, Gregg Losinski of Idaho Fish and Game told ABC News. The other man then tried to spray the bear as he was charging at him, but the bear attacked both of the man's hands.
The men managed to escape and other workers helped to transport them to Madison Memorial Hospital in Rexburg, Idaho, Losinski said.
According to a hospital nurse, then men suffered treatable but substantial injuries.
"The biggest worry is infection, as bears do not have clean teeth," Losinski said.
The second attack Thursday involved a mother bear defending her cub, according to the National Parks Service.
"When we have hikers that come upon grizzlies and they have a cub, the first thing the mother's going to do is try to defend those cubs," Yellowstone spokesman Dan Hottle told ABC News Radio.
A group of four people hiking in Yellowstone saw an approaching grizzly bear cub around 11:30 a.m., the parks service said. A sow grizzly then appeared and attacked two of the hikers, leaving them with bite and claw wounds. They managed to escape when the unharmed hikers discharged canisters of bear spray, scaring away the sow and her cub.
"They were following all the directions that we encourage people to do when they're in the back country, which is hike in groups, carry pepper spray and make noise on the trail," Hottle said. "Unfortunately, a mother with cubs in the park is the most dangerous animal we have."
All four members of the group were able to walk out of the trailhead, according to the parks service. One person was treated at the scene, while the second hiker was transported to a hospital by ambulance.
"It could have just been that they surprised her, walked up on her," Hottle said. "The first she's going to do is have her claws out and be ready, so it's lucky that they escaped the way that they did without serious injury."
ABC News' Ben Stein contributed to this report.