The list price was $1.125 million in August 2011, when Sotheby's International Realty held the first open house for 1674 Highland Oaks Drive, in the Los Angeles suburb of Arcadia. Scented candles burned, classical music played and the air conditioner ran as potential buyers milled through the home's three bedrooms, living room and combination den/dining room. Through sliding glass doors, a pool was visible in the rear garden; beyond it stood a sharply trimmed hedge. Past the hedge, in the ravine below it, a deep wash lay. Metropolitan Los Angeles ends at the edge of this canyon property, and above the wash, its steeply upland collar of national forest begins.

Once, like all the canyons threading the foothills of the San Gabriel Mountains, Santa Anita Wash had a stream tumbling through it, lined with coast live oaks, sycamores and mountain mahogany. In the dappled light of the understory grew coffee ferns, delphinium, phacelia, monkeyflowers. Bears gorged on blackberries while scrub jays jealously cached acorns. By day, the canyon was atwitter with finches and bushtits, and at night, the tree frogs and crickets chorused.

But on the day of the open house for what Sotheby's called its "Highland Oaks Beauty," there was no wild swell of twittering. No frogs, no crickets, no sign of a creek. The roughly 200 acres of sun-bleached concrete, gravel and sand in the canyon below resembled some kind of quarry. In a sense, that's what it was -- a pit gradually gouged out of the woodland over the last 85 years in an ongoing struggle to contain the mountains.

This was the front line between Arcadia and the notoriously sandy slopes of the San Gabriel Mountains, which in any given year, if it rained hard enough, just might bury what Businessweek Magazine routinely ranks as one of America's "Best Places to Raise Your Kids" under a roiling mix of rock, sand and water. Santa Anita Creek once flowed freely here. Now, there was a reservoir two miles upstream, then a debris basin to settle grit out of the released water, a concrete channel funneling clear water out of the basin, and a series of gravel-lined pits to filter and store it for later use in local kitchens and pools.

That summer day in 2011, a newly erected elevated conveyor stood alongside the debris basin, channel and pits. It was there to carry sediment from a scheduled cleanout of the reservoir. Beyond that, most of the eastern lip of the creek's steadily widening wash had been cleared for a sediment dump.

Back inside the house, asked about the potential for noise from the flood-control site, the Sotheby's agent said, "No, there's no noise." After a moment's thought, she reconsidered: "Wait a minute. There were some trees."

There were indeed some trees, most recently 179 oaks and 80 or so sycamores. They comprised such a rare remnant of old-growth riparian woodland that when the Los Angeles County Flood Control District bulldozed them eight months earlier to enlarge the sediment dump, the state's most famous tree-sitters climbed into the canopy. Actress Daryl Hannah protested at the gate. News helicopters thundered overhead.

Only later did it become clear that the skirmish was about more than just a single woodland. It was the catalyst for the far deeper and wider recognition that the Los Angeles County Flood Control District planned to bulldoze yet more wild places in more wild canyons, even in the Angeles National Forest, to dispose of a backlog of sediment from 13 other dams and 161 other debris basins. The felling of the Arcadia woodland, in effect, drew back the curtain on the magic trick that makes life on a floodplain possible for 10 million people. In the furor that followed the bulldozing of the oaks behind 1674 Highland Oaks Drive, not just environmentalists but also ordinary homeowners suddenly came to believe that L.A.'s Flood Control District had become as hardened as its paved river beds. In the process, it had gone too far, destroying what drew many residents to Los Angeles in the first place.

"Hell, we're giving away the land, we're selling the climate," quipped Elias "Lucky" Baldwin, who owned the ranch that back in the day encompassed Santa Anita Wash. The year was 1881, and the railways had just come to Southern California. The land rush was on. But one thing never made the fine print of the deeds: flood danger. After nine often-deadly storms washed through the Los Angeles Basin, a catastrophic flood in February 1914 drove so much silt into the San Pedro Harbor that ships couldn't dock. The Chamber of Commerce finally demanded action. Loss of life was one thing. Loss of business was another: The Panama Canal was just about to open up maritime trade to the Pacific as never before. In 1915, the Los Angeles Flood Control District was formed.

Flood Control's goal, as set down by James Reagan, its first engineer, was not just to protect the port, but also to render as much as possible of L.A.'s "non-operative" land commercially viable. By 1927, the Santa Anita Dam above Arcadia was completed, and the 13 other dams along the San Gabriels were either built or in the pipeline. Reagan told Angelenos that the only way someone at the port would even know about torrents in the mountains 40 miles away would be if they telephoned to inquire about the weather. The next year, however, St. Francis Dam failed just outside Los Angeles. The ensuing floodwaters killed hundreds. The heyday of dam building in Southern California was over.

The decline of new dams would have made more sense had other measures been taken to prevent flood damage. The notion of hazard zoning got such short shrift, observed Jared Orsi in his 2004 history Hazardous Metropolis: Flooding and the Urban Ecology in Los Angeles, that it amounted to none at all. Wetlands set aside to absorb seasonal floods don't pay taxes. Neither do parks. So when, in 1930, landscape design scion Frederick Law Olmsted Jr. and urban planning pioneer Harland Bartholomew presented a park master plan for Los Angeles that incorporated flood zones, noting that the land could serve for recreation during dry seasons, the Chamber of Commerce rejected it.

Slowing development was another option. But the opposite happened: Pushed by Southern California property barons, the federal Bureau of Reclamation agreed in 1928 to build what became Hoover Dam, near a then little-known Nevada railway town called Las Vegas. While this Mojave colossus wouldn't stop floods in L.A., it would provide all the water needed to keep building houses across the Los Angeles Basin. In 1936, part of the old Baldwin ranch was sold to a real estate syndicate led by Los Angeles Times publisher Harry Chandler. Reporting the acquisition, the Times extolled two things: old oaks and new water. "Winding drives among its oaks will lead to residential sites of from one to five acres, each marked out to include some of the noble trees."

The "noble trees" were coast live oaks, trees that are to the L.A. foothills what redwoods are to Mendocino. Back in Baldwin's day, oak woodlands provided the region's air-conditioning system. But as his land was divided up, housing tracts replaced the oaks. Five-acre lots advertised in 1936 became third-of-an-acre lots by 1951. To line the new suburban streets, post World War II subdividers planted lawn-friendly and water-hungry tropical trees. New, sun-drenched "ranch homes" had plate-glass windows along with plenty of power from Hoover Dam to run the now-necessary air conditioning.

Just before Colorado River water began flowing to Los Angeles in 1939, a series of catastrophic floods killed more than 100 people. Nobody wanted that in the real estate section of the newspaper. Aided by federal dollars and the U.S. Army Corps of Engineers, the Los Angeles County Flood Control District began building what Orsi's Hazardous Metropolis describes as "a Maginot line of debris basins along the front of the foothills." Beyond these stadium-sized catchments, rivers were narrowed, deepened, paved and fenced. The entire floodplain was fitted with curbside storm drains that fed into the paved rivers. The upshot: a Los Angeles County Flood Control District empire of not only 14 dams and 162 debris basins, but also 500 miles of channelized former river and 3,035 miles of storm drains.