IN the great tool chest of geology, Mother Nature reached for the Virgin River to chisel many of the steep-walled canyons and other sandstone spectacles that make up Zion National Park.
Now some of the river's tributaries are being considered as possible dam sites to meet the growing water needs of southern Utah.
The Washington County Water Conservancy District, which serves a rapidly growing area southwest of the park, has identified several potential dam sites above and below Zion.
But Park Service officials and environmentalists worry that such a move would alter the erosional processes that helped shaped the park and would affect wildlife and vegetation.
The tension reflects two fundamental forces of the West - water scarcity and wilderness preservation. It also symbolizes the emerging struggle over water rights outside national parks.
National environmental groups are already agitating over what they perceive as threats to water quality or quantity at more than a dozen park areas. These include proposed water-development projects in Florida near the Everglades, groundwater pumping near Death Valley in eastern California and southern Nevada, and geothermal wells near Yellowstone in Wyoming.
The stakes are particularly stark here. Southern Utah is one of the country's fastest-growing regions. A development ethic runs deep. But the area also harbors some of the nation's most coveted wilderness areas.
Projections show Washington County's population more than quadrupling in the next 50 years - from 50,000 today to 225,000.
St. George, a resort community southwest of the park, has doubled in population in 10 years. Thus county water officials are out with divining rods.
OF particular concern to the Park Service are two proposed dam sites upstream of Zion. One is just outside the park on the North Fork of the Virgin River, which runs through the Zion Narrows, a series of sheer red-rock canyons that offer some of the most spectacular hikes in the park (see photo, right). The other is on the East Fork of the river.
Park Service officials say that altering the natural flow of the river would threaten park "values," impact riparian habitat, and endanger fish such as the Virgin spinedace.
"When the park was established, one of the purposes was to preserve the natural process of canyon formation," says Zion Superintendent Donald Falvey. "If you put a dam in, you are interfering with that process."
Federal and state agencies are working with Washington County officials to find alternatives that will balance preservation values with water needs. It won't be easy.
Upstream sites hold pluses for the water district: The canyons around Zion offer the best dam locations, and the high altitude would mean less evaporation from reservoirs. Water officials also say there would be no adverse environmental impacts.
But because of what Ron Thompson, general manager of the water district, calls the "perception" of harmful impacts, he says the "first effort will be to take care of our water needs below the park."
Environmentalists, though, also oppose any reservoirs or dams that would impair the flow of streams there. "The Virgin is one of the last largely free-flowing rivers in the Colorado basin," says Ken Rait of the Southern Utah Wilderness Alliance. "It is part of an area that harbors an incredibly diverse array of plants and wildlife."