Grizzly bears are capable of running as fast as 40 mph.
Close encounters with hikers are a risk in the Yellowstone National Park area in Wyoming, Montana and Idaho, and park rangers recommend packing protection akin to mace for Manhattan muggers — bear spray.
The grizzly population of the Greater Yellowstone Ecosystem has more than tripled since 1987. About 150 call the park home. The bears were declared a "threatened species" in the lower 48 states in 1975. Grizzly relatives also reside in Alaska.
Non-lethal bear spray — carried in a cartridge resembling a small fire extinguisher — expels "a fine cloud of Capsicum derivatives to temporarily reduce a bear's ability to breath, see, and smell," according to the National Park Service.
That buys time for a quick escape from the agile beasts.
Grizzly bears are roughly 1 1/2 to 2 times larger than black bears, which also roam the area, according to the the park service. Grizzly males weigh between 200 and 700 pounds and females between 200 and 400 pounds.
Adult grizzly bears stand about 3 1/2 feet at the shoulder, can climb trees, run up and down hill, and swim.
That's why park regulations require that visitors to stay at least 100 yards away unless safely tucked in a motor vehicle.
And don't feed the bears!
While the odds of an attack are estimated at just 1 in 2.7 million in the Yellowstone area, a hiker can never be too careful.