The Durkee facility, Oregon's only cement plant, is operated by the largest U.S.-owned cement company, Ash Grove Cement. In 2008, the company reported $1.2 billion in sales. That same year, it also reached an agreement with the state of Oregon to cut its mercury emissions by installing a carbon injection system.

I visited Durkee in November, hoping to see the new $20 million mercury control system, reportedly in the initial phases of construction. But my request for a tour was denied. Jacqueline Clark, Ash Grove's head of public relations, e-mailed me that the Durkee plant was facing imminent layoffs and could not accommodate a tour. Indeed, a few months earlier, Ash Grove announced plans to halt production at its nine U.S. plants, including Durkee. (In early December, the company temporarily ceased production and laid off more than half of the plant's 115 workers.) Company officials said they might close the facility altogether if proposed federal regulations on mercury are enacted next year.

Although Ash Grove refused to allow a visit, Justin Hayes, the program director of the Boise-based Idaho Conservation League, suggested that a look at the facility's exterior might be instructive. So we made the hour-and-a-half drive from Boise on a warm afternoon. The plant itself is situated on the west side of Interstate 84, tucked into a steep-sided valley along a bend in the Burnt River.

Hayes has been key in the regional fight against mercury pollution. He has negotiated mercury reductions with large industrial players such as Monsanto, and his scientific sleuthing helped to reveal massive emissions from northern Nevada gold mines. Hayes is particularly concerned about the Durkee plant because metropolitan Boise, with its rapidly growing suburbs, sits less than 100 miles downwind. An avid fisherman, Hayes also bemoans the fact that many of the area's world-class fisheries have become mercury repositories.

On the way to Durkee, we passed the husk of the old cement plant at Lime, which operated from 1922 to 1980. Hayes commented that it would make a good set for a post-apocalyptic, Mad Max-type action film. He's right, but the site is unlikely to be used for anything anytime soon. According to the Oregon Department of Environmental Quality, its soil is heavily contaminated with PCBs, arsenic, residual petroleum and hydrocarbons –– the toxic byproducts of six decades of cement manufacturing.

A little past Lime, we pulled into a dirt parking lot outside the Durkee plant's main gate. Above us, a high-pitched metallic whine emanated from a conveyer chute: crushed limestone being transported from quarry to kiln. A layer of light gray cement dust — 4 or 5 inches deep — coated a concrete highway divider. Hayes scooped up a handful and let it pour out of his fist. "The dust control could be better here," he said. "Don't you think?"
 
Mixed with gravel, sand and water, cement becomes concrete, a material as ubiquitous and seemingly benign as you will find in the built landscape. It is fundamental to growth — strengthening structures, hardening highways and sidewalks, underlying our cities like synthetic bedrock. In 2008, American plants supplied a staggering 189 billion pounds of raw cement and clinker, a cement precursor. Although that figure represents a 30 percent decline from 2006, when construction was still surging, enough cement was made in the U.S. last year to spackle an area roughly the size of Delaware in pavement a quarter-inch thick.

Portland cement, the light gray powder found in everything from concrete to stucco, accounts for more than 95 percent of the cement produced in the U.S. The recipe for creating it has changed little in 150 years. It still requires mountains of calcium carbonate or limestone, which, in eastern Oregon, tends to be loaded with mercury derived from the region's history of volcanism. Volkswagen-sized chunks of the rock are blasted loose, hauled in goliath front-end loaders and fed into a series of crushers. Then the limestone fragments are powdered and mixed with metal oxides that help determine the cement's compressive strength and hardening time.

This mixture is then sent to massive kilns — some as long as football fields — which reach temperatures of at least 2,500 degrees F. During heating, the limestone is chemically transformed into "clinker," pebble-like pellets that are mixed with a little gypsum and ground into the fine flour we know as cement. The process releases large quantities of carbon dioxide and — in the case of Durkee — vast amounts of mercury vapor. Mercury is also released from the coal burned as fuel in the kiln, but the amount is minuscule compared to what's baked out of the limestone.