For a time, scientists believed that Nevada's valleys, with few exceptions, harbored geologically isolated reservoirs of water. Around 50 years ago, however, evidence began accumulating that the carbonate blocks in multiple valleys are hydrologically connected. (Connections also run through the basin-fill. According to a recent study by the U.S. Geological Survey, at least some water from the basin-fill in Spring Valley may be leaking into Snake Valley through a limestone formation that spans the adjacent Hamlin Valley.)

Today, scientists recognize a number of large regional flow systems. In the Death Valley system, for example, water streams south from the Nevada Test Site, across the Amargosa Desert, right through the Funeral Mountains. In the Great Salt Lake Desert system, it falls from the crest of the Snake Range into Snake Valley, then flows north into Utah. The White River/Muddy River Springs system, for its part, starts not far from the city of Ely and flows south, towards the Colorado River. Because everything is so connected, critics say, the Southern Nevada project has the potential to affect springs at surprising distances, not only in Nevada but also in neighboring Utah.

For a couple of days, Sada and I follow the carbonate, leaving the Death Valley flow system to pick up the White River/Muddy River system northeast of Las Vegas. Then, in Snake Valley, we shift to the Great Salt Lake Desert system. It is a singular fact that these flows through the carbonate underlie surface features carved by ancient waterways. Today, for example, the White River flows only intermittently, but before the last Ice Age ended, around 10,000 years ago, it gurgled its way through a good half-dozen grassy valleys, ultimately joining with the Colorado River. Lake Bonneville, the Pleistocene predecessor of the Great Salt Lake, was once 135 miles wide, 325 miles long and up to 1,000 feet deep, making it a tad larger than present-day Lake Michigan. At its maximum, Bonneville reached far into Snake Valley, where traces of its shoreline can be seen today.

As we drive along, Sada tells me a little about himself. He grew up in Bishop, Calif., not far from Owens Lake, which famously went dry after Los Angeles commandeered the flow of the Owens River. Perhaps that's one of the reasons why, for as along as he can remember, he's been drawn to water. At first, he says, he dreamed of working in the ocean as a marine biologist; then he switched to the study of freshwater lakes and streams. Eventually, he became enchanted by the small, improbable upwellings of water scattered across the Great Basin, one of the driest landscapes on earth. An applied ecologist, he frequently conducts research for government agencies and public utilities, including the National Park Service and the Los Angeles Department of Water and Power.

The Border Inn sprawls across the Utah-Nevada state line like a mirage. It's a frequent gathering place for locals opposed to the Southern Nevada Water Authority's water-export plans. It's also a convenient stopover for visitors to nearby Great Basin National Park, which is dominated by the snow-streaked face of 13,167-foot-high Wheeler Peak, the highest mountain in the Snake Range. Here, Sada meets up with Krissy Wilson, the native aquatic species coordinator for Utah's Division of Wildlife Resources. "I am so pleased to meet you," she exclaims. "It's like you're the king of mollusks, the god of snails!"

The next day, Wilson takes Sada and me on a day-long tour of the major springs on the Utah side of Snake Valley. With her quick sense of humor and master's degree in biology, she proves an excellent guide. The distance we cover is great: Snake Valley is nearly 100 miles long and, in places, well over 15 miles wide. It's not yet known how sensitive the springs here may be to the withdrawal of water on the Nevada side. But already the Utah Geological Survey has placed monitoring wells along the flow-path groundwater takes through Snake Valley. The objective is to keep an eye on water levels at increasing distances from the pumping stations, watching for declines that could impact not only springs but also agricultural and domestic wells.

Wilson first stops at Gandy Warm Springs, where crystalline waters gush from hidden caverns on the shoulders of the northern Snake Range. Lush vegetation (including purple loosestrife, a colorful invasive) grows along the water's edge while damselflies and dragonflies swoop overhead. Unstrapping his sandals, Sada wades in, with Wilson directly behind him. A minute or so later, the two stop beside a waterfall that cascades down a ferny wall. Sada scoops up a few springsnails, all exemplars of the species, Pyrgulopsis saxatilis. "They're so small!" Wilson exclaims. They are also rare. Like Pyrgulopsis anguina, the species Sada found at Big Springs, Pyrgulopsis saxatilis appears to be restricted to Snake Valley. In August, to the delight of the pipeline's opponents, the Fish and Wildlife Service indicated it would consider both species for endangered or threatened status, which could raise an additional hurdle to the pipeline project.

Before its brook was diverted, Wilson says, Gandy Warm Springs used to flow into the Gandy Salt Marsh, a spring-fed wetland that sprawls across the valley floor below. Each spring, this small oasis, supplied by water from the basin-fill, connects with a seasonally flooded playa. In response to this ephemeral expansion, little fish known as least chub swim into the playa to breed. The females are lemony in color; the males, green and blue, with a gold racing stripe painted on each side. Once widely distributed across northwestern Utah, the species today exists in just six locations, three of them in Snake Valley. It, too, is a candidate for federal protection.
A springs complex resembles a grove of trees in a discontinuous forest. It is only when you piece the fragments together that the extent of biodiversity is revealed. Thus, the least chub at Gandy may be the same species as those found at the Leland Harris complex around 30 miles away, but they are genetically distinct. Their DNA reveals their geographical isolation. The last time least chub from the Gandy Salt Marsh and neighboring Bishop Springs mingled their genes with those at Leland Harris was around 10,000 years ago, Wilson says, at the end of the last ice age. Left alone for long enough, these chub could give rise to new species.

The Gandy Salt Marsh illustrates a point Sada has been making. While the springs that tap the carbonate tend to be the largest and most spectacular, those with sources in the basin-fill are also biologically important. And, says Sada, "They may well be more vulnerable." In apparent response to a recent multi-year drought, for example, a number of Gandy's 50 or so small, cool-water springs slowed their rate of flow, and some stopped altogether.