Historic American Engineering Record: San Carlos Irrigation Project, North and South of Gila River, Vicinity of Coolidge, Pinal County, Arizona

Historic American Engineering Record (HAER) No. AZ-50 presents a written historical summary and relevant historical documentation about the construction and use history of San Carlos Irrigation Project (SCIP) waterways and features, which deliver Gila River water to central and southern Arizona for agriculture, industrial, and residential uses. The report contains a narrative description, photographs, drawings, and maps.

Authorized under the San Carlos Act (43 Stat.475), SCIP is a joint Indian and non-Indian irrigation and water delivery project that includes 100,000 acres, of which 50,000 are Indian lands in the Gila River Indian Reservation and 50,000 are private or public, non-Indian lands in the Florence-Casa Grande Valley in Pinal County, Arizona. The SCIP began with the construction of Coolidge Dam along the Gila River. At present, SCIP features fall into two classifications: irrigation system and power system features. The irrigation system consists of storage reservoirs, storage and diversion dams, canals, distribution systems, irrigation wells, and pumping plants. The power system is made up of generating stations, transformer stations, transmission lines, and distribution lines.

Foremost, the San Carlos Irrigation Project is historically significant for creating an integrated irrigation system to serve both Indian and non-Indian lands along the Gila River. Prior to project construction, irrigation of area lands was piecemeal and non-Indian agricultural development above the Gila River Indian Reservation depleted water supplies for native communities. Native communities and people suffered increased water shortages as non-Indian settlements grew along the river above Pima lands during the latter half of the nineteenth century. Diversions of Gila River water to irrigate non-Indian farms caused great hardship and widespread poverty among Pima families, who previously enjoyed a very successful agriculturally-based economy. Initial authorization of the project in 1916 and the passage of the San Carlos Act on June 7, 1924 culminated years of studies and efforts to develop water storage on the Gila River and restore water to Pima Indian communities.

The project also incorporates a number of individual infrastructure features that have engineering significance. These features include Coolidge Dam (see HAER No. AZ-7 at https://core.tdar.org/document/393145), Sacaton Dam, and China Wash Flume. Ashurst-Hayden Dam, the primary diversion facility for the entire system, is an important structural feature. Finally, SCIP irrigation and power features as a whole are significant as representations of an evolving, dynamic irrigation project. SCIP feature types and feature construction document changes in irrigation system technology and design through many decades.