South of Fort McMurray, swaths of trees were removed to make way for an underground oil pipeline that carries product from the oil sands mines to processing facilities. (Michael S. Williamson/The Washington Post)

Fort McMurray, Canada — The Keystone XL pipeline wouldn’t start anywhere near this boom town in northern Alberta, but the oil sands here are the prologue to any talk of a pipeline.

These vast oil deposits — about 173 billion barrels of economically recoverable reserves — would feed the Keystone XL. Yet the huge amount of energy needed to produce oil here, and thus the greenhouse gases produced in the process, are at the heart of opposition among various U.S. environmental groups to the pipeline.

Unlike oil that spurts up from reservoirs in most of the world, half of this stuff is dredged up in a process more akin to strip mining, with massive open pits. Layers of earth are clawed away and then the companies working here dig into a rich layer of oil sands –- or tar sands as it is called among those who want to make it sound less appealing. It is also known as bitumen, the thickest type of petroleum — thicker than molasses, in fact. It does not flow freely and can turn solid at relatively moderate temperatures.

We got our first look courtesy of Shell, one of several companies working here. The boreal forest, thick with trees, bushes and wetlands, lines the highway. Twice we crossed the Athabasca River, which winds north. Then the scenery gives way to fields with trees and top soil scraped away, to administrative buildings, one of the largest private air fields in North America and massive processing plants that are tangles of pipes and tanks — or pots and pans, as one company worker put it. We passed a dormitory that houses 2,500 workers, each in a private room with a television and gym access and a lounge where they can get a drink or watch movies. (Some company dorms are dry.)

The pits are the main attraction. Each one can be as deep as 120 meters, or nearly 400 feet. From a mushy ridge where our boots sank into the black sands, we peered at Shell’s Jackpine mine pit. (Jackpine is the name of a common tree in the area.) Trucks the size of a couple of townhouses looked small as they ferried back and forth inside.

The extraction of oil from these sands isn’t complicated in concept and the process hasn’t changed since it was patented in the 1920s by University of Alberta scientist Karl Clark. Essentially, the oil sands are mixed with warm water. The sand sinks to the bottom, the water and suspended clay sits in the middle, and the oil floats on top. A centrifuge removes the remaining water from the oil. The process sucks up a lot of energy and water. Trying to make do with less is a major challenge for the companies.

Also, the scale of the operation is daunting. Inside the giant mines, about 15 trucks, each one twice the size of a large house, lug 400 tons of the black sands to conveyer belts that feed into a series of processing facilities, which mix the sands with warm water, skim off the oil and spit what’s leftover into dark tailings “ponds” the size of small lakes.

The tailings contain water, fine silts, leftover bitumen, salts and solvents used during the separation process. Shell recycles 83 to 87 percent of the water in the tailings ponds, but still draws water from the Athabasca River. Fred Kuzmic, Shell’s environment manager, said the company uses only 30 percent of its allocation and hopes to reduce that further. Kuzmic said that enough bitumen would sink and seal the tailings ponds, but environmental groups say the ponds leak. Recently the federal environmental agency, Environment Canada, required new testing. We met Nicolette Stanley, a Shell employee who takes samples from the company’s more than 170 ground water monitoring stations.

We had a look at an old, used up pit at Shell’s Muskeg River mine, which the company is turning into a tailings pond. The provincial environmental ministry says that the tailings ponds for the oil sands so far cover an area slightly larger than the District of Columbia. The companies and provincial authorities note that that might seem large, but it’s a tiny portion of the province, which is two-thirds bigger in area than California.

The payoff for all this: For every one of those big trucks carrying 400 tons of oil sands, the companies get 200 barrels of oil. With crude oil selling for $80 to $100 a barrel, that’s very profitable. Shell does its own internal evaluations of project economic viability using a hypothetical carbon price of $40 a ton, well above current prices on Europe’s carbon exchange, and the oil sands still pass financial muster, John Abbott, head of Shell’s oil sands operations, said on the phone after we finished our tour.

Can the gigantic gashes in the earth here be repaired afterward? The reclaimed areas won’t be as flat for one thing; the ground, now less compact, will be higher. From interviews today and earlier, it seems that it is difficult, if not impossible, to reconstruct the wetlands that provided a good home to this unusual type of forest. Still, some companies are trying, albeit  on a small scale. The Pembina Institute, a think tank, says only 1 percent of the tailings ponds has been replanted. Shell officials pointed out mounds 130 to 200 feet high of “overburden,” top soil layers scraped away and stored for future restoration.

Cheryl Robb, a media relations person at Syncrude, took us for a look at her company’s efforts to reclaim some areas transformed by mining, and we walked up to a scenic (and buggy) overlook. A field of young trees — jack pines, aspen, spruce — was springing up above a small idyllic pond. Small cannons sounded just over the hill to scare off birds that would be harmed by toxic oil residue and other substances if they landed in a tailings pond. And you could hear the trucks and buses barreling down the highway nearby. In the distance, you could see the stacks and pipes of a processing facility.