STANISLAUS NATIONAL FOREST -- Perched atop a charred ridge, scientist Brad Rust stares at a tiny bead of water -- which sits, motionless, glistening like a perfect pearl in a sea of ash.
The soil does not absorb the droplet, it repels it -- a finding that tells Rust and his colleagues that fierce winter rains could rush down these hillsides burned barren in the 257,000-acre Rim Fire, flushing dirt, rocks and ash from one of California's most pristine watersheds.
With Saturday's rain portending the onset of storm season, the race is on to study, repair and restore the damage from the blaze that began Aug. 17, but won't be contained until Oct. 1 and will likely be fully extinguished only by winter's rain and snow.
"Soil is a big sponge and a big filter," said Rust, one of 75 experts brought in to work with the U.S. Forest Service's Burn Area Emergency Rehabilitation teams. "If water goes down the hill, there will be erosion."
Nature will recover, but it may take a decade or two, said the rehab experts. Already, a black bear was seen eating a burned deer. Ponderosa pine cones are scattering seeds and ferns are sprouting from firefighters' water. Ants are emerging from deep underground. Western pond turtles are scuttling through a spared meadow.
But an ashen Tuolumne River -- designated a "Wild and Scenic River" by Congress -- could be deeply damaging for both wildlife and humans. Native fish species like rainbow trout can't see to feed on bugs and sediment abrades their fragile eyes and gills. Downed trees and other debris could capsize boats and snag swimmers.
Computer models of water runoff estimate that the flow in some stretches, such as the junction of Granite and Cherry creeks, could more than quadruple, from 80 cubic feet to 380 cubic feet per second. A cubic foot is basketball-size volume of water.
The Rim Fire, the largest one in Sierra recorded history, has damaged some camps, undermined miles of wilderness roads, claimed a historic 1930s-era National Forest Guard Station and threatened Native American artifacts, according to the Forest Service's rehabilitation teams.
Several camps popular in the Bay Area -- Mather, Tawonga and San Jose City Camp -- were damaged, but only Berkeley's Tuolumne Camp was destroyed.
Water is still clear at Yosemite's Hetch Hetchy Reservoir. The fire licked at its southern flanks, and landslides and erosion are a threat this winter. The reservoir feeds San Francisco and other Bay Area communities and was fiercely defended by firefighters.
The blaze is slowing as it creeps deeper and higher into the rocky reaches of Yosemite and Emigrant Wilderness, said Yosemite fire education specialist Gary Wuchner.
But the scientists are most concerned about the erosion that lies ahead.
"For the fish and wildlife in those creeks and rivers, it could be a major concern," said Eric Wesselman, executive director of the Tuolumne River Trust. "And this is the playground for millions of people, with special campgrounds, hiking trails and swimming holes, used for many years."
Two burn-rehab teams of scientists -- one with the U.S. Forest Service, the other with Yosemite National Park -- are rushing to conclude their research by Tuesday to support federal funding requests.
It will cost several million dollars to stabilize roads, rebuild trails and fend off the weeds, such as yellow star thistle and spotted knapweed, that invade after a fire, according to Todd Ellsworth, who is leading the Forest Service's recovery campaign.
Fires are part of the landscape's natural history. But ancestral fires tended to just creep along, slowly burning through the underbrush, leaving trees -- ponderosa pine, sugar pine, Douglas fir, incense cedar, white fir, black oak -- largely unharmed.
Contemporary fires can burn very hot because of dry winters and accumulations of underbrush, incinerating huge old trees that can't recover. Heat especially mounts when a slow-burning fire lingers on the land.
The fire burned so hot in some areas -- five times hotter than boiling water -- that it changed soil chemistry and structure, the rehab team found. Of the 256,895 acres that burned, an estimated 17,910 acres are identified as especially hot, "high burn" areas, which are more erosion-prone.
And these hot fires have another unique characteristic, detected by Rust and other soil scientists: Their gases carry wax from so much burned foliage. When the gases condense, the wax clogs the soil pores. That pearly droplet of water simply sits on the soil beneath the ash.
"Water will come down, hit that, then sheen off," Rust said. "The surface soil structure is all destroyed."
The waxy layer will linger for two seasons or so, he said. Then the landscape will recover because just a few inches down, the soil remains healthy, rich with microbes.
The speed of the fire -- burning through 30,000 to 50,000 acres in just two consecutive days -- may have saved much of the landscape, by jumping over creeks and only singeing the ground, and creating a mosaic of life and death.
While the burn rehabilitation program has been in place for several decades, the increased availability of satellite and remote sensing technologies in the past decade has led to major advances in the way the U.S. Forest Service rapidly maps areas burned by wildfires. These tools save time and increase accuracy, leading to faster analyses and better recommendations.
The new technologies are used to create burn severity maps, essential for accurate computer modeling of runoff and erosion risk. But equally important is field work by scientists like Rust, whose mission is to "ground truth" the satellite observations. He can recommend measures such as protective ground cover.
Then, focus will shift to the next chapter in the life of this ancient wilderness: restoration.
"Once the fire is out, the spotlight goes away," said Wesselman of the Tuolumne River Trust. "For the rest of us, those who work and live in the watershed, that is when the real work for us begins."
Contact Lisa M. Krieger at 650-492-4098.
256,895 (401 square miles): Acres burned
84 percent: Containment, as of Saturday
11: Residences destroyed
3: Commercial property buildings destroyed
Cost to date
Popular campgrounds along the Tuolumne River -- a green strip surrounded by black -- are largely intact but may be dangerous due to dead trees.
"God's Bath" swimming hole, cherished for its granite cliffs and cold deep emerald water, was preserved.
Some Native American areas burned, such as sites with rock mortars and scatterings of flaked stone toolmaking material, but can be protected.
A historic U.S. National Forest guard station was destroyed.
Rock Garden Rapids, a favorite among kayakers, is threatened by a downed tree. Winter kayakers can float the South Fork of the Tuolumne River but should be aware of hazardous trees.
Critical habitat for rainbow trout and yellow-legged frogs in the Clavey River may suffer from erosion, but were outside the "high burn" area. Less essential waterways, such as Granite Creek, lost willows and alders that keep water cool for fish, frogs and turtles. Happily for humans, much poison oak was lost.
The two main paved access routes -- Cottonwood and Cherry Lake roads -- will remain closed until repaired. Lumsden Road also is closed.
Source: U.S. Forest Service Burn Area Emergency Rehabilitation team and firefighting teams
HOW TO HELP
The Tuolumne River Trust, with offices in San Francisco, Sonora and Modesto, is seeking donations to help restore stretches of the river not repaired by the federal government. To help, go to www.tuolumne.org/content.