TUOLUMNE, Calif. — Tourists stopped at the Rim of the World overlook on California 120 earlier this month to take photos of the panoramic view — just as they always have.
But they stared in silence at the ashen hues of a landscape swept by the largest wildfire to burn in the Sierra Nevada in more than a century of recordkeeping. Steep canyon walls and mountain slopes that had been robed in chaparral and oak were now draped in black, spreading to the horizon in a funereal scene.
To the north, miles and miles of forest were still and lifeless, the earth scoured by flame. Millions of charred trees stood naked, their needles incinerated.
The huge Rim fire, ignited Aug. 17 by a hunter's illegal campfire, is likely to have transformed large swaths of the Stanislaus National Forest for decades to come.
Remote sensing satellite images indicate that virtually all of the vegetation is dead on nearly 40% of the area of the 401-square-mile blaze, which burned from the national forest into the western portion of Yosemite National Park, where it continues to smolder.
Burned chaparral and oak will quickly resprout. But where large patches of trees were killed, ecologists say it could take 30 to 50 years for the forest to reestablish itself in the shrub fields that are the first to grow. If there are more fires in the meantime, the land could permanently convert to chaparral.
"You're looking at a huge area that doesn't have any living conifers," said Hugh Safford, regional ecologist for the U.S. Forest Service. "The big question really for managers and the public is what's that landscape going to look like in 50 to 100 years. It's going to look really different."
The fire started in chaparral midway up Jawbone Ridge on a Saturday afternoon not far from the Rim overlook — thus its name. Flames sprinted up the canyons into higher elevations. On a couple of days with high winds, the blaze grew explosively, racing through more than 30,000 acres in a single day.
The fire chewed through expanses of ponderosa pine and other conifers. It charred young tree plantations that had been planted after previous wildfires. It scorched some of the last remaining old growth in the Stanislaus, downed power lines and crept up to Hetch Hetchy Reservoir, the source of San Francisco's water.
Like all wildfires, it was temperamental. Sometimes it burned furiously, sometimes slowly and sometimes barely at all. That has left a mixed palette of black, brown and green within the fire boundaries.
About 29,000 acres were largely untouched by flame, according to the vegetation survey, which compares remote sensing images of the burn area with images taken before the fire.
Two weeks ago, dozens of federal scientists from around the country set out to assess the damage and plan emergency recovery efforts. They fanned out across the forest, digging holes to see if the soil would hold water or repel it in erosive sheets. They checked trails and roads and known archaeological sites.
They tramped through plantations and forestland that had been previously thinned or burned in managed fires to see if the treatments had succeeded in taming the flames.
Curtis Kvamme, a Forest Service soil scientist who was on his fifth day of poking in the dirt, took a shovel to scrape a thin layer of ash from the ground in an area of badly burned timberland. With his gloved hands he carefully exposed the soil, then squirted water in a zigzag pattern onto the ground and watched what it did. It beaded.
"High repellency starts at about 3 inches," he told his colleague, Kellen Takenaka, who was recording the information in a small hand-held computer.
Kvamme's verdict: The soil had burned at high severity, meaning there is a greater chance of erosion. Instead of seeping into the earth, rainfall or snowmelt could wash in torrents downslope, potentially contributing to flooding.
"This is cooked, a lot of acres burned pretty intensely," said Todd Ellsworth, a Forest Service watershed manager who oversaw the post-fire survey, known as Burned Area Emergency Response. The team will recommend steps, such as straw mulching, in areas with a high potential for erosion and runoff that could damage roads or clog streams and rivers with sediment.
When the soil survey results were released a few days later, the findings were better than expected. The soil had burned at high severity in only about 7% of the Rim blaze. The ground burned at low severity or was unburned in 56% of the acreage.
But those numbers don't reflect what happened above ground. Satellite imagery reveals hardly a speck of green on one block of 33,593 acres of trees and shrubs. On one 16,445-acre patch of conifers, nothing appears to have survived.
Severely burned tree patches that big leave a paucity of seed sources, making it that much harder for the forest to regrow.