Wide-open spaces and burly, gas-guzzling automobiles go hand in hand in the West. After all, how else can you get to your favorite climbing crag or hiking trail?

Perhaps by driving a burly rig that guzzles a lot less gas. Or so California and a handful of other Western states had hoped. But the U.S. Environmental Protection Agency recently shot down California's efforts to cut tailpipe greenhouse gas emissions by 30 percent. Agency head Stephen Johnson argued that the state's regulation would lead to "a confusing patchwork of state rules" and would be less effective than a measure in the 2007 federal energy bill requiring new vehicles to average 35 miles per gallon by 2020. California officials say their rule would beat that - 36 miles per gallon by 2016.

The agency's move skunked 17 other states that had pledged to adopt California's standards, including Arizona, New Mexico, Oregon and Washington. Most of those states have now joined Gov. Arnold Schwarzenegger in a lawsuit to overturn the EPA's decision. California's fight may be bolstered by a new study from Stanford University, which concludes that global warming can increase asthma and respiratory disease in already-polluted areas. Since California has six of the nation's dirtiest cities, researchers say it suffers even more than the rest of the country from the rising temperatures attributed to greenhouse gases.

Demand for gasoline and wide-open spaces in the West doesn't look like it's going to slow down any time soon, as the region's population continues to boom. Six of the 10 fastest-growing states are Western, according to the latest figures from the U.S. Census Bureau. Nevada topped the list, while Arizona, Utah and Idaho ranked second through fourth, respectively. California accrued the second-highest number of new residents last year - about 300,000.

Keeping all those new Westerners fed may prove challenging. A recent survey from the U.S. Department of Agriculture finds that nearly 11 percent of Americans are "food insecure," meaning they don't know where their next meal is coming from. New Mexicans suffer the second-highest rate of food insecurity - 16.1 percent - in the country (Mississippi's rate is 18.1 percent). Compared to 1996 figures, California and Washington have seen slight drops in the number of hungry citizens, while in Utah, despite the primary religion's emphasis on food storage, about 4 percent more people now don't have enough to eat.

Explosive growth has some policymakers worried about air quality and water quantity in the West's major urban centers. An air quality council in Denver, Colo., says it will be impossible for the state to curb Front Range air pollution quickly enough to avoid breaking federal limits on ozone - a nasty component of smog that can cause asthma and other ailments - for the second summer in a row. Meanwhile, some Colorado water managers are clamoring for a greater voice in limiting development. The state is expected to gain 3 million new residents by 2035, but current and planned water projects will supply only 80 percent of that projected growth, and climate change is a wild card that may leave many newcomers high and dry. Democratic state Rep. Kathleen Curry is pushing a bill that would force developers to provide stronger proof that enough water will be available for the bluegrass lawns and hot tubs of their new subdivisions. In California, Orange County is facing up to the reality of water shortages - a new $500 million "toilet to tap" plant will purify up to 130 million gallons per day of treated sewage.

National parks are also feeling the sting of growth. Airborne ammonium, a compound associated with industrial feedlots and fertilizers, is showing up in greater concentrations in Western national parks, including Rocky Mountain, Yellowstone and Glacier, according to a recent National Park Service report. The nitrogen-rich compound can harm wildflowers and insects, alter lake chemistry, and even change forest structure.

Also a potential hazard in national parks: Forty-seven U.S. senators, led by Mike Crapo, R-Idaho, recently signed a letter asking Interior Secretary Dirk Kempthorne to lift the ban on carrying loaded guns in national parks and wildlife refuges. Park Service regulations require that weapons be carried in an "inaccessible" way, while the BLM and Forest Service defer to state gun laws. Other Western signers included Max Baucus, D-Mont., Jon Tester, D-Mont., Larry Craig, R-Idaho, Mike Enzi, R-Wyo., John Barrasso, R-Wyo., Pete Domenici, R-N.M., Wayne Allard, R-Colo., and Jon Kyl, R-Ariz. The senators' letter said, in part, "These regulations infringe on the rights of law-abiding gun owners, who wish to transport and carry firearms on or across these lands."