This report describes the results of archaeological investigations undertaken northeast and in the vicinity of the Tator Hills at the southern edge of the Santa Cruz Flats. The archaeological investigations were funded by the Bureau of Reclamation, Arizona Projects Office, and identified as Tasks 43 and 45 of Contract 3-PA-30-00740. The work was conducted to mitigate the impact to prehistoric resources in the construction of the Central Arizona Irrigation and Drainage District, Central Unit IV irrigation system. Three sites, two Archaic campsites (AZ AA:6:18[ASM]) and AZ AA:6:19[ASM]) and one Hohokam resource procurement locus (AZ AA:6:17[ASM]), were investigated. The primary goal of the study was to describe and elucidate the Archaic occupation of the Santa Cruz Flats. AZ AA:6: 17(ASM) was utilized by the Hohokam as an intermittent gathering and processing camp. The presence of a redware vessel in addition to plainware ceramics suggests that the site dates during the Sedentary or Classic periods. The occurrence of fire-affected rock and ground stone artifacts indicates that food processing and preparation were the primary functions of the site. Characteristics of the ground stone assemblage are reflective of a small-seed economy suggesting that native plants were the principal resources exploited at the site. AZ AA:6: I8(ASM), named the Tator Hills site, is considered to be a campsite that was intermittently occupied from the Middle Archaic to the Protohistoric or Historic period (ca. 2500 B.C.-A.D. 1800). Sixty-nine cultural features were documented at the site, including thermal pits, fire-affected rock concentrations, aboriginal surfaces, and a structure. The exposure of a Late Archaic activity surface, with accompanying thermal pits, ground stone artifacts, and a brush shelter, provides new insights about the composition of Archaic seasonal campsites. Later Ceramic period manifestations were primarily superficial in character, and appeared focused on the exploitation of plant resources along the drainages that crossed the site. In all likelihood, the site was occupied by small, mobile bands throughout time, who utilized the area as part of a seasonal round, most likely in response to resource availability. AZ AA:6: 19(ASM), named Coffee Camp, represents a significant site on the Santa Cruz Flats. Excavations at the site revealed stratified cultural deposits which extended from the Late Archaic to the Protohistoric period and indicated that the site was repeatedly occupied for more than 2,500 years. The major occupation occurred during the terminal Late Archaic (ca. 2200 to 1900 B.P.). Represented among the 369 cultural features documented at the site were habitation structures, both inhumation and cremation burials, and various types of cooking, storage, and processing pits. Artifacts from the site included chipped stone, ground stone, ceramics, and shell. Some of the ground and chipped stone artifacts were recovered from caches, and the ceramic artifacts represent some of the earliest securely dated materials of their type in the Southwest. The features and artifacts documented at the site, such as the presence of early ceramics, cremations with grave offerings, architectural variety, and a large, possibly communal structure, indicate that radical changes were occurring in Late Archaic culture. Primary among these was the emergence of a bi-seasonal settlement-subsistence system that entailed a primary, intensive focus on the abundant floral resources of the floodplain/riverine environment with secondary support derived from short-term exploitative activities in lower/upper bajada locations. This economic organization, as well as items of material culture, may be considered precursors to subsequent Hohokam manifestations in the deserts of southern Arizona.