San Diego — Silverio De La Mora Ceballos is hard to spot among the ten-foot-high reeds of this pristine section of the Tijuana River.

"Pristine" isn't a word you think of when you talk about the Tijuana River, but here at the head of its valley, in the Sub-delegación La Presa area just below the Rodriguez dam, it gurgles clear and gently over the rocks and sand and among the reeds. A few soda cans, car parts, and cardboard boxes are strewn around, but looking east, words that come to mind are "rustic," "pastoral," "bucolic."

Now look west, and see the future. The river has been completely covered in concrete, a continuation of the concrete that downtown tourists cross by footbridge on the way to Revolución Avenue.

De La Mora, a Tijuana electrical contractor, has joined the fight to roll this progress back. He not only wants the concrete torn away and replaced with more eco-friendly rock berms and greenery, but he's campaigning to surround these upper reaches with a thousand-acre urban forest. A set of "lungs" for air-polluted, tree-starved Tijuana.

He says he's paid a price for joining a public campaign against the plans of the state government. He says all his electrical contracts with the state government have dried up. Despite being a one-time friend of the substitute governor, Alejandro González Alcocer, De La Mora says he is now unemployed, frozen out by the people who were once his steady customers.

Yet all he's doing, he says, is fighting for what Mexico's president has already decreed as federal policy.

"Fifteen years ago, under President Miguel de la Madrid, an urban forest and nature preserve was precisely the federal government's promise," he says. "But then PAN [the business-oriented National Action Party, or Partido Acción Nacional] came to power, and now money dictates everything."

The floods of 1980, 1983, and 1993 also dictated the state government's action. At the height of those floods, when waters from the dangerously full Rodriguez dam had to be released, they caused multiple drownings downstream, and many houses were destroyed. The concrete canalization is at least partly the state and municipal government's response to those concerns.

But De La Mora believes the state government is more interested in profit: in maximizing land-use in this central part of the Tijuana valley. According to a state government spokesperson, its aim is to sell off what was once federal government land to private buyers, to build shopping malls and residential housing instead of creating a forest.

"And ordinary people will not be able to afford the houses," he says. In the end, he believes the area might result in more maquiladora factories.

We're down in the river. Bull rushes, an occasional flight of birds with bell-clear warbles surround us. One strange bird lets out a mocking call like an Australian kookaburra.

"I don't know the names of these plants or birds," De La Mora admits as we splash through the last surviving patch of reed forest, "but I feel close to them in my heart. These plants are the same as you have in the Imperial Beach Tijuana River estuary. It's the same region, the same ecology. But except for right here, [the state government] has killed all this natural life with their concrete canalization project. It wasn't necessary, but they want to squeeze the river. Minimum space for the river, maximum for land-developers."

De La Mora and fellow campaigner Felipe Daniel Ruanova Zárate lead the way across a mini-dam of loose rocks held together by wire mesh. The water chuckles underneath.

"Civil engineers call this a 'gaviones' structure," says Ruanova. " 'Gaviones' is a collection of rocks held in place by wire mesh without use of concrete. It slows down the velocity of the water in flood time. If [the state government] had been thinking in a good way, they could [use this system] and preserve the river as a green area without any hazard to the environment."

Ironically, Ruanova is the engineer who originally oversaw the development of the entire Río area of Tijuana. He was sent from Mexico City by the federal government. "I was the general director of the PRODUTSA [Promotora del Desarrollo Urbano de Tijuana, or Urban Development Promotion of Tijuana]. We had to pave these roads, put trees in, sewage in, throw bridges across the river -- five for cars, five for pedestrians, to develop this."

One thousand acres of the 3000 acres that make up the Río area, he says, had always been laid aside for the "urban forest," a permanent green area in the tercera etapa -- the third developmental area in the upper reaches of the river valley. He knew the idea was safe because President de la Madrid, along with state and municipal authorities, had issued a decree assigning the land "in perpetuity" as a territorial reserve exclusively for ecological purposes.

But since the PANistas' accession to power in Baja California, in state and city governments, claims Ruanova, this highly valuable area has become a pawn in the bargaining between the nationally dominant PRI (Partido Revolucionario Institucional) government and locally strong PAN leaders.

Ruanova decided to fight back after outgoing president Salinas de Gortari "donated" about 120 acres of the urban forest land for the state to develop commercially in 1994. Ruanova could see it was the beginning of the end for the preserve, that money and greed would chip away at the 1000-acre wilderness. After all, it did sit in the middle of the country's most wildly expanding city.

On June 10, 1995, on Radio Z13, a Tijuana talk-radio station, Ruanova announced that he was forming the "Front for the Defense of the Woods of the Tijuana River" (Frente de Defensa del Bosque del Río Tijuana).

"After the radio broadcast, Silverio and others joined," says Ruanova. "And we did a huge campaign. In the first stage we had 10,000 letters sent to the state governor, Terán Terán. He never gave us an interview. Then in our second campaign we got more than 100,000 signatures asking [Mexican] President Zedillo not to give this land away for commercial purposes."

He is still waiting for a response on that petition.

"I had left the government in 1984. The only reason was because the people from the PAN didn't like me. This business of making a forest in the middle of our city is not business-oriented. Nobody makes money out of it."

But why is it so important? Ruanova and De La Mora climb back uphill toward Monte de los Olivos cemetery. "This is what we're fighting for," De La Mora says, turning to look down the valley. Under the high "mares' tail" clouds, a thin, mustardy-yellow haze sits vaporous and still over the valley. "That," he says, "is L.A. pollution. From L.A.! And it's usually worse."

Engineer Ruanova explains. "Of course, we have our own pollution too, from cars, maquiladoras, and other industry. Tijuana has been named the fourth or fifth dirtiest city in Mexico. But so much comes from Los Angeles and Long Beach! They produce toxins from refineries and factories and hundreds of thousands of vehicles. We are importing -- tax-free! -- lots of toxins in the air from the States."

He says winds bring the pollutants down, to bounce off Point Loma, usually sparing San Diego, and then get sucked up the Tijuana River valley. "Tijuana sits between two lines of hills. They create a funnel effect. The predominant winds come from the northwest. The toxins are heavier than air, so they tend to come down in the lower parts of the valley. Where the river is. There is always a dark cloud there.

"This is why we're fighting to plant trees in the tercera etapa, because we need to mitigate that pollution, to have the trees metabolize those contaminants."

"We Tijuanans didn't have the education to put in trees around our houses, in the places where we live," says De La Mora. "So now we have shameful statistics to live with."

Ruanova quotes them. "The United Nations recommends that there should be between 7 and 13 square meters of trees and green area per inhabitant," he says. "We in Tijuana have far less than one square meter of green area per inhabitant. Actually 0.26 of a square meter per citizen. In San Diego you have almost a hundred times that! You have between 18 and 22 square meters per inhabitant."

"I think it is more," says De La Mora. "Between 35 and 40. Whatever, it is much, much more."

He says San Diego escapes much of the L.A. effect by luck and design.

"San Diego has the privilege of the protection of Point Loma, and also San Diegans have made [their own] microclimate, because they have planted so many trees and green areas. You fought back. We didn't. That's what we insist: this needs to be a treed area of woods. Your Balboa Park is a good example."

"And there's one other thing," says Ruanova. He points up to the narrow canyon that leads to the Rodriguez dam, just out of sight.

"The curtain [wall] of this dam is built precisely above a tectonic fault, named La Nación-San Ysidro. Sometimes when it is full, the dam holds 137 million cubic meters of water. It was built around 70 years ago. If you are intending to build 10,000 houses for residential-commercial purposes in the flood-plain below, you're talking about the potential for a huge disaster. But if you put trees in instead and the dam bursts, they slow the water. They can be washed away, but you can always replant."

Ten minutes later, Ruanova guns his '89 Ford down a sloping ramp. Suddenly we're sweeping along the concrete Tijuana riverbed at about 30 mph, probably the speed of floodwaters. Today, only the center channel has water in it. We dust past abandoned armchairs, tires, and trash, then climb back up the other side near a sign.

"Tercera Etapa Río Tijuana: Un Lugar Para Ti. The Third Stage of the Tijuana River [development]. A place for you." It's a pro-development sign put up by the organization Ruanova used to run, PRODUTSA. Except PRODUTSA is now run by the state government.

"We who live here in Tijuana know that [this area] is the only place the city has to grow," says PRODUTSA's spokesperson, Licenciada Rosa Elena Moreno Garcia. "We have no choice. We have the United States on the north, Rosarito and Ensenada to the south. And the federal government gave the area to the state because they want [them to act] to protect the area from flooding."

Moreno says the state government is selling the land to private buyers, not to make a profit but so the Japanese-funded flood-control project is self-financing.

No industry will be built in the area, she says, and residential sites will be sold at prices within reach of the ordinary person.

She adds that a wooded area, "Parque Morelos," is already operational, and has just had its size increased from 60 to 90 hectares, about 222 acres -- just under a quarter of the area Ruanova's group wants.

As for earthquakes, she feels the risk is small to people living in the new district. "The San Andreas [fault] is not exactly on the site of the city. It is 50 to 60 kilometers out. Tijuana doesn't suffer many earthquakes."

She says that, with a city growing by 85,000 each year, space for people is as important as mitigating air quality. "We have to take it from both sides, the human, and nature. We have to protect both." The concrete canal, she says, is, above all, to protect people.

Back at the Tijuana River, De La Mora and Ruanova are pinning their hopes on a vote coming up in two weeks in the state congress in Mexicali on stopping the state's commercial development of the tercera etapa.

Ruanova is confident. "We will win," Ruanova says. "Then perhaps we can plant a forest and breathe easier."