NEWARK, CALIF. -- The bulky white mountain commands all of the attention in this industrial neighborhood on the eastern edge of San Francisco Bay, overshadowing the dusky pink water and the downsized, shamrock-green trains shuttling back and forth on their portable track.

At 100,000 tons, the mountain is a shadow of its future self, and its growth is the focus of round-the-clock labor.

This is harvest time in the salt ponds lining the bay, the busiest time of year for Leslie Salt Co., whose goal is to amass a 700,000-ton mountain of salt before winter rains come to northern California, probably late this month.

The harvest, and the five-year cultivation that preceded it, follow a pattern laid out in ancient times but used at only a few sites in the United States today to tap solar power to extract salt from sea water.

That pattern is being modified constantly, not only to accommodate technological advances but also to adapt to the peculiarities of each season's harvest, according to John Pyles, Leslie's solar operations manager, who supervises the harvest.

"No two years are ever the same," Pyles said, recalling variations in weather and technique that have marked his 13 harvests.

Salt has been harvested commercially from the bay for about 140 years, starting in 1850 with the influx of prospectors intent on finding gold. The newcomers were desperate for salt to preserve their food, Pyles said, and the first crops of salt reaped from the bay sold for $50 a ton, about double the current price.

In the years that followed, about 30 small salt works sprang up around the bay, making salt so plentiful that the price plummeted to $2 a ton, forcing decades of contraction in the industry that, by 1936, left Leslie the only producer in the Bay Area. Harvesting was a pick-and-shovel operation then, as it was in the salt mines of the eastern United States, with the crop hauled away on horse-drawn carts, Pyles said.

Today, special harvesting equipment has taken over, but the basics of the cultivation and harvest remain the same.

This fall's crop was sowed five years ago when, during high tides, rising bay water flowed into pipes that carried it across levees and into the first in a series of "concentrating" salt ponds. Left largely to the influence of sun and wind, the water began the long gestation period needed to build up its salt content. Watching the early years of cultivation is, one Leslie official said, "as exciting as watching water evaporate."

The company's five "watermen" intervene occasionally to transfer the water through Leslie's system of gates and pipes to other ponds where salt-making continues. By the time the salt water is moved into the ponds nearest the main plant, 90 percent of the water is gone, leaving "pickle" or saturated brine so saline that further evaporation would turn it into salt.

Each April, the brine is spread into crystallizer beds and spends the summer hardening into a thick, crunchy mass that looks like fresh, white, sleet-covered snow that has been splashed with water tinted a deep pink by microorganisms that flourish there.

As fall approaches, Pyles said, "everybody gets itching to go," to haul out the harvesting machines and start the 24-hour, five-day-a-week race to gather the salt before the first big rains. The work force, about 20 people during the rest of the year, expands to nearly 100.

They tackle one 40-acre crystallizer bed at a time, commanding harvesting machines with whirling blades that loosen the salt and scoop it into waiting boxcars. Portable train tracks give the small fleet of locomotives access to every corner of the pond, as workers in the field simply move the tracks in the direction that they want the cars to go. When full, the trains head toward the main plant and the mountainous salt pile to unload and begin again.

Most of Leslie's salt eventually will be used to make caustic soda for industry. The rest will be manufactured into salt licks for animals and food-processing agents or table salt for humans.

"It's a strange type of agriculture," observed Barry Nelson, executive director of the Save San Francisco Bay Association, a group that studies the bay and the migratory birds that seek food in Leslie's salt ponds. He considers the salt ponds a plus for birds and wildlife, many of which seek shelter there from the relatively harsher tides and storms of the bay.

The birds can tell from afar which salt ponds hold food that appeals to their species, said Barbara Ransome, Leslie's environmental manager. Nature's color-coding system makes it clear to humans, too, that the ponds are not alike. Different microorganisms in the water are primarily responsible for turning some ponds chocolate brown, some green and others pink, she said.

The birds generally stay away from a 400-acre storage pond that holds bittern, the highly concentrated salt solution left at the end of the harvest, she said. Nevertheless, Nelson's group considers the presence of the toxic byproduct in the bay the only environmental concern generated by Leslie's salt-making activity.

The company is seeking new markets for its bittern, some of which is sold to firms that use it to control dust on back roads in the Northwest's logging country, she said. Other prospects, still in experimental stages, include a program to use bittern to scrub the stacks of coal-fired power plants, curbing acid rain.

Despite the potential for growth in bittern sales, the primary product for Leslie, a subsidiary of Cargill Inc., remains salt -- 1.25 million tons of it a year, about 5 percent of U.S. production, being harvested here and at two smaller plants near the bay.

That translates to 6,000 tons a day pulled from Newark's crystallizer beds during harvest season and added to the expanding salt mountain next to the main plant. It represents enough hard work, Pyles said, to make everyone weary as the harvest moves toward its final days and to push one question to everyone's lips: "They say, 'Oh, God, when's this thing going to end?' "