Historic Distribution. The Bonneville Basin within Utah encompasses the area that was covered by ancient Lake Bonneville and which, today, lies within the Great Basin physiographic province of North America. The entire Great Basin province is distinguished geologically by its characteristically parallel north- south mountain ranges that are separated by broad, alluviated desert basins and valleys (Xxxxxxxxxxxx 1951). In Utah, the steep, gravelly slopes of these ranges are prominently marked by benches and other shore features of Lake Bonneville. Numerous springs are present at the base of the mountains (Xxxx 1966) and in the valley floors. Several aquatic species have maintained an existence as relict populations in these springs, including the least chub, Columbia spotted frog (Rana luteiventris), and several species of mollusks. Populations of these species, however, are rare and in some areas declining. The rapid deterioration of these aquatic environments, primarily from water development and/or agricultural practices, has caused other unique Bonneville Basin species, such as Rhinichthys osculus relictus a subspecies of speckled dace, to become extinct (Xxxxx et al. 1974).
Historic Distribution. The historic distribution of the Virgin spinedace is not well documented. Xxxxxx (1977) speculated that historic occurrence was in most of the clearwater tributaries and several mainstem reaches of southwestern Utah, northwestern Arizona, and southeastern Nevada (Figure 1). Museum records from the University of Nevada at Las Vegas, Xxxxxxx Xxxxx University, University of Michigan Museum of Zoology, and the United States National Museum support Xxxxxx (Addley and Xxxxx, 1993; Cross 1975; Xxxxx, 0000; Xxxxxx et al., 1991). The earliest survey records indicated this species was common in the Santa Xxxxx River and North Fork of the Virgin River, but probably less common in the Virgin (Xxxxxx (1932, 1936). X.X. Xxxxx (unpub. data) collected Virgin spinedace near Bunkerville, Nevada, in 1938, but surveys in 1942 in the same area lacked Virgin spinedace (Cross, 1975). Furthermore, the species was absent from surveys below Littlefield, Arizona between 1942 and 1975 (Cross 1975).
