-Aravaipa Creek in Graham and Pinal counties, Arizona, is a nowisolated, spring-fed tributary of the San Pedro River. This stream acts as a refugium for 7 of the 12 known native fish species of the San Pedro drainage (Gila robusta, Rhinichthys osculus, Agosia chrysogaster, Tiaroga cobitis, Meda fulgida, Catostomus insignis, and Pantosteus clarki). Only two introduced fishes are present (Ictalurus melas and Lepomis cyanellus), and these are restricted to a pond lateral to the creek. Increasing demands on water in the American Southwest, along with changes in land use, possibly climate, and other factors, have had adverse effects on the native aquatic fauna (Miller, 1961, et seq.). A substantial percentage of natural marshes, springs, and streams already are modified beyond reclamation; only a few enjoy relative immunity. In addition, animals in the West have been increasingly subject to competition from a myriad of exotic animals (Miller, 1961; Deacon, et al., 1964; Hubbs and Deacon, 1964; and others). All this contributes to marked modification of the distribution and abundance of native fishes, and to their decline and extinction in some instances. One of the few aquatic habitats that has maintained relative virginity is Aravaipa Creek, Graham and Pinal counties, Arizona. In this paper we record some collections of fishes from that stream, including results of our intensive survey of the fishes between 6 November 1964 and 1 May 1965. Charles H. Lowe and Wallace G. Heath, University of Arizona (the latter now at Western Washington State College), studied Aravaipa Creek in the 1950's, with special reference to thermal ecology of the fishes. Results of their studies are soon to be published elsewhere. TOPOGRAPHY AND GEOLOGY OF THE AREA. Aravaipa Creek drains the northwest end of a structural trough that to the south holds the Willcox Playa (a remnant of Pluvial Lake Cochise; Cole, 1963), and the extreme headwaters of the south-flowing Rio Yaqui of Mexico. It originates at a low divide about 1,310 meters (m.) above mean sea level, passes northwest for 75 linear kilometers (km.) (ca. 140 km. by actual stream channel), to enter the now-dry San Pedro River at an elevation of 660 m., 16.8 km. south-southeast of Winckleman, Arizona (Fig. 1). Only about 50 creek-km. of the channel holds permanent surface water.