The Great Basin is defined by hydrology and physiography. It is a region of interior drainage bounded prominently on the west by the Sierra Nevada and the Cascade Range and on the east by the middle Rocky Mountains and the Colorado Plateau. Less distinct are its northern boundary with the Columbia Plateau and the southern transition with other subdivisions of the Basin and Range province. It encompasses most of the state of Nevada, while its Utah portion is set off physiographically by the Wasatch Mountains and the high plateaus, particularly the Pavant, Tushar, and Markagunt sections.

In terms of geological plate tectonics, the Great Basin may be viewed as a series of north-south trending, linear, fault-block mountain ranges occupying the distance between the Sierra crest and the Wasatch Front. They may have rumpled up in response to the impact of the Pacific plate on the continental California coast. The block faulting began in the middle and late Tertiary period and still continues. Abrupt front slopes and more gentle back slopes are typical; and the intervening valleys are structural rather than erosional.

A strict hydrologic definition of the Great Basin would move its boundaries back to the headwaters of all streams draining into it. Following the Sevier, Provo, and Bear rivers would extend the Basin deep into the high plateaus and the Uinta Mountains. A strict structural definition might place the Basin boundary at the major fault lines, usually buried in piedmont alluvium of the prominent mountains and plateaus facing the Basin. Generally, some physiographic compromise is most serviceable in dealing with the history of man in the region.

Three distinct natural environments are encountered in crossing the Great Basin. Playas are undrained mud or salt-encrusted flats resulting the from deposit of sedimentary material as the lowest part of the basins fill. During wet seasons they may shimmer with shallow, ephemeral lakes. Climbing upgrade, alluvial fans of sand and gravel are deposited by runoff from above according to the speed and volume of water available. The many canyon exits merge their fans into extensive bajadas and piedmonts. The source of the material is the mountains--uplifted, tilted fault blocks usually with a steep front and more gentle backslope. Bare rock and cliff may still outcrop along the crest as a mountain is gradually reduced to alluvium.

The Great Basin is effectively cut off from the westerly flow of Pacific moisture. Orographic uplift of crossing air masses by the Sierra and the Cascades provides cooling and precipitates much of the moisture out. The result is a BSk (Dry Steppe cold) climate classification for most of the Basin in the Koeppen system. The climate is typical of middle latitude, semi-arid lands where evaporation potential exceeds precipitation throughout the year. There is no water surplus or stream originating in such a climate, and mean annual temperatures are under 64.4[[ring]]F (18[[ring]]C). Oases occur where highlands generate surface streams or springs. By the time air masses reach the Basin's eastern edge they get another lift, creating extra moisture and highland climates that support Utah's population corridor below. High-level, low-pressure systems affecting Utah weather at the precipitation maximums in spring and fall are often referred to as "Great Basin" or "Nevada" lows.

The vegetation response to the Great Basin's climate, soils, and topography can be generalized in a look at its life zones. Plants range from Upper Sonoran sagebrush-grasslands through Transition (Foothill) sagebrush, juniper, and piñon to Canadian (Montane) pockets of aspen-fir on prime mountain range locations. Soils grade upslope from Aridisols through Mollisols with occasional young Entisols appearing on the fans, floodplains, and valley bottoms. Interior basins are commonly around 4,000 to 5,000 feet above sea level and ranges as high as 10,000 (and occasionally 12,000 feet) in elevation.

Remnant "sea" or lake erosional features such as beaches, seastacks, bars, and spits seem curious anomalies throughout the Great Basin. They are remains from huge Pleistocene lakes filled in an era of melting glaciers and a wetter climate. The Great Salt Lake is a remnant of Lake Bonneville, while Pyramid Lake and Carson Sink (the western terminus of the Humboldt River) are remnants of ancient Lake Lahontan. Government geologist G. K. Gilbert and surveyor Howard Stansbury first mapped and interpreted many of these features.

The modest Humboldt River (less than .9 million acre feet and 17,000 square miles of watershed) meanders and arcs its way across north-central Nevada. It is the only stream of notable distance or consequence originating in the Great Basin. (Of course, if you are looking for water in an arid land any seep or stream is of consequence!) It provided a route for the California Trail to the gold fields after 1849 but had been used by 1841 as a California branch of the Overland Trail. In 1826 famed Trapper Jedediah Smith traced the southern route through the Great Basin to Los Angeles and found his way back across the heart of the Great Basin in 1827. He disproved the existence of the mythic Rio Buenaventura that was said to flow to the sea and which had appeared on many previous maps. Thus the "basin" concept began to take form in the public mind. Trapper Peter Skene Ogden explored the Basin from the north in 1828, but Joseph R. Walker retraced Smith's route within a year, going on to central California and publicizing the Humboldt trace.

John C. Frémont's major government exploring expeditions of 1843-44 and 1845 crossed the Basin by both Smith's and Walker's routes. The Unknown, Mary's, or Ogden's River was renamed by Frémont for the famous German geographer and naturalist Alexander von Humboldt. It was Frémont too who coined the term "Great Basin" and helped imbed the reality of the drainage and physiography in the public consciousness. Meanwhile, the Humboldt River, often crossable without even a wet boot, was becoming the route of choice for the 49ers and the "highway of the West."

Though emigration slowed, the transit corridor became more important. In 1868-69 the Central Pacific crews raced across the Basin to meet the Union Pacific at Promontory, Utah. U.S. Highway 40 followed from the 1920s to the 1950s and after the 1960s Interstate 80 made only minor adjustments in the route. Many of the railroad towns, established to provide water in the steam era, became regional supply places for area ranching and mining. The freeway's bypass system strengthened some towns, dried up the lifeblood traffic of others, and physically obliterated a few of these basin oasis towns. Route doglegs that may at first seem odd and out of the way remain the most cost-effective connection between points, as they utilize the low passes between ranges and the meandering route of the Humboldt River.

Anglo settlements in the Basin often sprang from Mormon State of Deseret colonization efforts. The Mormon-established Basin towns still had rows of tell-tale poplars as late as the 1950s. Native Americans had for generations lived a finely balanced hunting-gathering lifestyle tuned to the local resources. Transportation nurtured more stable population centers. Ranching was a dispersed endeavor throughout the Basin, and mining towns flourished and disappeared from the 1870s to 1930s. By the 1980s many of the old districts had revived through new technology (particularly open-pit mining of finely disseminated deposits and large-scale heap leaching in the Nevada Gold Belt), but long commutes to towns with core services are now the norm.

Historical "sites" are generally more linear and route oriented than point or site oriented due to the nature of the Great Basin as a transit corridor and a topographically broken semi-arid land. Most are associated with the major themes of transportation, mining, ranching, and national defense.

In Utah, Promontory Summit is a railroad transportation time machine of major significance, the stuff of dreams. The old air force base at Wendover housed and trained the crews who dropped the atomic bombs on Japan that dropped the curtain on World War II. Dugway Proving Grounds, Tooele Army Depot, and Hill Air Force Base are testaments to more than four decades of the Cold War. The Tintic Mining District is another superb time slice for the epic story of mining in the West. Bingham's remarkable open-pit copper operation remains a landmark. Callao is a rough-hewn and remote ranching remnant. The Pony Express route, the forgotten West Desert winter sheep range, and critical isolated wildlife and bird refuges also could be mentioned.

For many, the Great Basin is an affair of the heart and soul that grows with intimacy. It has to do with a psychology of open space and an appreciation of the Great Basin as a place. The two opposing points of view were challengers in the 1980s with the proposed MX "racetrack" missile system. They will likely surface again in the 1990s on the issues of electronic warfare and hazardous waste disposal.

Gary B. Peterson