More than 12,000 opponents of the proposed Keystone XL oil pipeline encircled the White House in Washington, D.C. on Nov. 6, weeks before President Obama's expected decision on what's become an iconic environmental battle. Running to the Gulf of Mexico from Alberta's oil fields, the pipeline would cut through the Great Plains and threaten oil spills into the Oglalla aquifer, the single largest source of fresh water in the United States. Though federal permits haven't yet been granted, landowners on the pipeline's path have been threatened with eminent domain land seizures; the federal review process has been corrupt, steered by oil company executives with insider connections and industry-hired consultants. Despite those problems, however, Keystone XL probably wouldn't be so controversial if it carried oil from old-fashioned, stick-a-tube-in oil fields. It doesn't. Alberta's vast oil deposits are dirty and hard to reach, mixed into sand or locked deep underground. Recovering the oil is a hugely energy-intensive process, multiplying its climate footprint at a moment when extreme weather is getting worse. And if the probabilistic links between climate and weather feel fuzzy, there's nothing nebulous about the apocalyptic landscapes that Albertan oil extraction leaves behind. Primeval forests and bogs are denuded and drained, replaced by barren slopes and toxic ponds. It may take centuries for life there to recover. "It is surreal," said Jennifer Grant, who directs the oil sands program at the Pembina Institute, an Alberta-based environmental conservation group. "It is such a vast area. From the air, you can see over 170 square kilometers" — 65 square miles — "of tailings ponds alone. It's astonishing to see the sheer scale." On the following pages, Wired.com takes a tour of Pembina's tar sands photographs. Above: A Very Big Pit Image: Suncor's Millennium Oil Sands Mine. The yellow spots at upper right are among the largest trucks in the world. (David Dodge/Pembina Institute)

The Boreal Forest Alberta's boreal forests are part of a subarctic biome that crowns North America. Growing on land shaped and scraped by glacial scouring, many of its plant and animal communities have evolved undisturbed since the last ice age. Boreal wetlands are a critical breeding habitat for almost half of all bird species found in the United States and Canada. Image: Boreal forest along the Athabasca river. (Pembina Institute/Flickr)

Tar Sands Mining Unlike conventional, easily accessible oil deposits, tar sands petroleum is mixed with sand and clay and water, creating a thick slurry that is trucked to processing centers for refinement. Roughly one ton of sand is needed to produce one barrel of oil, and the Caterpillar 797B trucks used to carry tar sands are the largest in the world. Water used in refinement — a mix so toxic that waterfowl die after landing in it — ends up in tailings ponds, which often leak. Image: The Athabasca river (top left) runs by a Suncor upgrading facility and tailings ponds. (David Dodge, CPAWS /Pembina Institute/Flickr)

Tar Sands Mining: The Extent According to the Pembina Institute, tar sands mining now occupies an area of about 260 square miles. The total minable region is roughly 770 square miles. Image: Boreal forest edges a Suncor surface mine. (David Dodge, CPAWS /Pembina Institute/Flickr)

Tar Sands Drilling While surface mining gets the most attention, most of Alberta's tar sands are locked in deposits too deep to access with truck and shovel. Instead these are extracted by a process of drilling and steam injection that forces oil to the surface. "The drilling companies say, 'We're after the deeper oil. We don't have the same footprint.' But that's not true," said Grant. "It pollutes more. It's going to fragment a much larger area with pipelines and roads and facilities. It will fragment an area that's dominated by wetlands. Scientists say it's actually as impactful as the mining." Image: Nexen's Long Lake facility. (Pembina Institute/Flickr)

A Big Footprint Canadian government-approved drilling permits already cover 30,000 square miles of forest and wetlands, said Grant, and could ultimately span 50,000 square miles — an area larger than Ohio. Image: Pembina Institute/Flickr

Jobs Tar sands oil comes at a steep environmental price, and there's controversy over how many jobs would be generated by the Keystone XL pipeline -- but especially in Alberta, there are direct and immediate economic benefits. Image: A sign in Fort McMurray, Alberta, the city closest to the tar sand surface deposits. (David Dodge/Flickr/Pembina Institute)

Unknown Limits Tar sands mining has grown faster than expected "and as a result they couldn't put environmental protection plans into place — wetlands policies, contaminant limits," said Grant. "What concentrations of pollutants are acceptable in the Athabasca river? What limits will protect air, land and water? We're continually now playing catch-up. Nobody has that information." Image: Tailings ponds. The Athabasca River flows past in the upper left corner. (Jennifer GrantPembina Institute/Flickr)

Restoration Though oil companies and government officials say mined lands will be restored, that's easier said than done — if anyone is even trying. Drained wetlands don't refill easily, and forest communities that evolved for thousands of years are very different than tree plantations. Out of the 260 square miles mined so far, less than one square mile has been certified as reclaimed, Grant said. Image: A Syncrude reclamation site. (Pembina Institute/Flickr)

After Keystone If President Obama rules against Keystone XL, it won't stop tar sands mining and drilling, but building other pipelines won't be easy. The leading post-Keystone candidate is the Enbridge Northern Gateway Pipelines Project, which would run from Alberta to the coast of northwestern British Columbia. Indigenous and coastal fishing communities will likely oppose the intrusion. "I feel like it's not a project that will be easy to get approval for," Grant said. Image: A Syncrude upgrader. (David Dodge/Pembina Institute/Flickr