A bird's eye view of fossil-fuel workhorses (photos)

Ever wonder where your electricity comes from? Coal provides about half of the electricity generation in the U.S. and more in some countries, such as China. Here's the San Juan Generating Station in the Four Corners area of northern New Mexico.

Coal is the cheapest way to produce power in the U.S. Environmentalists have pressured electricity provider PNM to clean up this decades-old plant or replace it. The utility says replacing the plant would be expensive and that it has recently installed controls to reduce harmful air pollutants, such as mercury, sulfur dioxide, nitrogen dioxide, and particulate matter.

Images in this slideshow were taken from a plane piloted by EcoFlight out of Farmington, N.M. For a related story, see "Take an aerial tour of fossil-fuel country."

Here is a closer view of a different power plant, the Four Corners Power Plant in the Navajo Reservation, just a few miles away from the San Juan Generating Station. As the plumes of steam from the smokestacks show, power generation from coal uses a lot of water, a concern for the southwest which is the midst of a multi-year drought. Coal is mined on site (you can see the coal piles at the bottom of the photo). The Four Corners plant is operated by the Arizona utility APS.

The very large digger in this photo gives an idea of the scale of the mining necessary to supply nearby coal plants. These coal mining operations go on for miles and have been operating for decades.

In addition to air pollution, coal-fired power generation also produces sludge as a combustion by-product. In the San Juan basin, that coal ash is kept in ponds and dried through evaporation. In theory, the coal ash can be recycled and used in production of other materials such as asphalt or gypsum boards, but doesn't happen. Local activist Mike Eisenfeld of San Juan Citizens Alliance is concerned that the coal ash contains radioactive materials.

Coal not only provides energy for electricity production, it also harbors natural gas. The San Juan basin is home to thousands of wells for coal bed methane--methane gas trapped in coal seams. Methane is the main component of natural gas, which is used for heating or electricity generation.

Here is one of the estimated 30,000 well pads in the San Juan basin which has as many as 30 wells per square mile, according to activist Mike Eisenfeld of San Juan Citizens Alliance. One major concern: the impact these roads have on the ecosystem. Since the area gets very little water, vegetation does not grow back quickly as it does in other parts of the country, Eisenfeld said.

The pump jacks in this area (see on bottom right of photo) are mostly used for pumping out brackish underground water, according to Wally Drangmeister, the director of communications for the New Mexico Oil & Gas Association.

Extracting natural gas from unconventional sources, such as coal beds, has contributed to a boom in new drilling techniques such as hydraulic fracturing, or "fracking," and horizontal drilling. During my tour of the area, an industry representative said the risk of contaminating water supplies via fracking is very low. Local activists are pushing the industry to disclose the chemicals it uses during fracking as well as regulations on how water used and produced during drilling is disposed of.

Although a desert area, this area of the San Juan basin is also home to agriculture just a few miles from two giant coal plants and thousands of gas wells. This image shows the circular irrigation sprinklers that draw water from the aquifer or the nearby San Juan River.