Sunlight streams through a dense canopy, casting a shimmering glow on a stream that dips under a well-traveled park road.
"I call this the kill zone," said Moose Mutlow, a contractor with the Yosemite Institute. "Animals crossing here just don't stand a chance."
Mutlow has studied the park's roadkill and found that hundreds of the very animals visitors come to see -- such as squirrels and black bears -- end up dead on Yosemite's busy byways.
It's easy to see why: In national parks and wildlife refuges across the country, tourists gawking at towering granite faces or roaring waterfalls often speed eagerly from one sight to the next, giving wildlife little chance to scurry out of the way.
Tennessee's Great Smoky Mountains National Park is the nation's most popular, with more than 9 million visitors annually. It harbors turkeys, possums, groundhogs and bears in its half-million acres of mountainous forest.
But when those critters wander onto a park-managed commuter road linking two nearby towns, the mix of speed and heavy traffic can be deadly. The park records about two traffic-related bear deaths a year, on average, spokeswoman Nancy Gray said.
"Speed is a factor," Gray said. "A lot of time, people are trying to get somewhere a lot faster than they should, and they're in wildlife habitat."
Rural and suburban drivers know that coming across a deer on a dark road is not unusual. But speeding through a landscape teeming with wildlife, as many national parks are, can have much more dramatic consequences.
"Depending on the season, people are more likely to see a dead animal than a living one," said Roger M. Knutson, author of "Flattened Fauna: A Field Guide to Common Animals of Roads, Streets and Highways."
Mutlow started his unofficial research after being ticketed -- twice -- for speeding through the park on his commute to teach at the institute, which offers visitors environmental education programs. The park ranger who caught him going more than 20 mph over the posted limit told him the signs were there to protect fauna. A curious Mutlow decided to do his own research.
Armed with a clipboard, a baseball bat to kill suffering animals that were obviously not going to recover from their encounters with cars, and a shovel to pry flattened victims from the blacktop, Mutlow spent 290 days surveying 30 miles of highway twice daily.
He found 250 animals, including squirrels, possums, skunks, coyotes, deer and bears, classifying them according to his "Appearance Index Matrix" -- a subjective scale that ranges from "victim appears to be sleeping in a poorly chosen location" to "victim resembles badly molded pancake," and "victim disassembled and spread liberally around area."
It all started as a joke, Mutlow said, but the research convinced him the problem was serious.
Great gray owls, endangered in California, like to nest and hunt in the park's open meadows, but can cross paths with hasty drivers as they swoop low for prey. Sixteen have been killed by cars since 1966 -- the last one recorded in 2005.
"It's a significant source of mortality for this species in the park," said lead wildlife biologist Steve Thompson. "And we think there are more than we hear about."
Last year, there were 15 collisions with bears reported in Yosemite, and at least two bear deaths. Most of the animals are females or young males forced out of prime habitat into more disturbed areas by older males, Mutlow said.
In the grassy wetlands south of Montana's Glacier National Park, so many western painted turtles are run over that observers might wonder if drivers take them for speed bumps.
The turtles cross the highway to get to ponds on the other side. With up to 500 cars an hour traveling at 70 mph or more, it's easy to see why many don't make it, said Kathleen Griffin, a University of Montana researcher studying the problem with funding from the state's Department of Transportation.
Over three years, Griffin counted 1,040 dead turtles along four miles of U.S. 93. The turtle isn't endangered, but it's important to the local Salish and Kootenai tribes because of its role in their creation myths, Griffin said.
She's looking into ways to keep the turtles safe as transportation officials expand the two-lane highway to three or four lanes. Fencing stretches of the route and guiding the turtles into underground culverts is one possible solution.
"Our whole road system affects wildlife, period," she said. "We're just trying to minimize the impact."
Some species have learned to avoid cars by changing their behavior, biologists say.
Grizzly bears, listed as a threatened species since 1975, are known to cross U.S. 2 near Glacier early in the morning, before the traffic picks up. They also run across roads, and when the volume increases to about 100 cars per hour, the bears stop crossing altogether, said John Waller, a ranger at Glacier who has studied the impact of area roads on grizzly habitat.
But while the bears had figured out how to protect themselves from cars, they were falling victim to another threat -- a railroad that follows the highway. The grizzlies are attracted by grain leaking from the rail cars on their way to West Coast ports. About two grizzlies are killed each year by speeding trains.
In Yosemite, officials are developing a campaign called "Red Bear, Dead Bear," which will post street signs around the park marking with a red bear the spots where bears have been killed, hoping to educate visitors rushing from one waterfall to the next.
After seeing so much carnage, Mutlow has repented. He shakes his head as another driver speeds over Ribbon Creek.
"Drive a little slower," he said. "It'll add five minutes to your trip, but hey, you're here to relax."