State of Arizona, complainant v. State of California, Palo Verde Irrigation District, Imperial Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, California, City of San Diego, California, and County of San Diego, California, defendants : the United States of America and State of Nevada, interveners : State of Utah and State of New Mexico, impleaded defendants : report / Simon H. Rifkind, special master

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274 tion of 107,588 acres and for the satisfaction of related uses, whichever is less, with priority dates of March 3, 1865 for lands reserved by the Act of March 3, 1865 (13 Stat. 541, 559); November 22, 1873, for lands reserved by the executive order of said date; November 16, 1874, for lands reserved by the executive order of said date, except as later modified; May 15, 1876 for lands reserved by the executive order of said date; November 22, 1915 for lands reserved by the executive order of said date.33 BOUNDARY DISPUTE-OPINION A dispute concerning a portion of the west boundary of the Colorado River Indian Reservation arose between the United States and California when the United States sought to establish irrigable acreage within that Reservation. An Executive Order of May 15, 1876,34 established the "west bank of the Colorado River" as the boundary of the Reservation. The United States contends that this language established a permanent, unchanging boundary denned by the west bank of the River as it existed in 1876.35 California contends that the language established a changing boundary, denned by the west bank of the River as it may exist at any point of time.36 Since the Colorado River has in this area moved eastward since 1876, California's contention, if sustained, would reduce the amount of irrigable acreage within the Reservation below the amount claimed by the United States. In the alternative, the United States contends that if the west bank of the River as it presently exists is held to be the correct boundary, then certain land west of the present 33The evidence does not permit greater specificity regarding priority. S4U. S. Ex. 505. 35U. S. Brief, pp. 31-35. 86Calif. Proposed Findings and Conclusions 18D: 112-18D: 209.