This rule finalizes the boundaries for the portion of Clark County, Nevada that is designated nonattainment for the 8-hour ozone national ambient air quality standard and designates the remaining portions of Clark County, including portions of the Moapa River Indian Reservation and the Fort Mojave Indian Reservation, as attainment for the 8-hour ozone standard. In a final rule published April 30, 2004, EPA had previously announced that all of Clark County would be designated nonattainment for the standard. EPA subsequently deferred the effective date of that designation to provide the State, affected Tribes, and EPA time to determine whether an adjustment to the boundaries of the Las Vegas nonattainment area was appropriate. Based on additional analyses submitted by the State and the Moapa Band of Paiutes, we conclude that the boundary of the Las Vegas nonattainment area should be adjusted. Through this notice we are revising the designations for Clark County to reflect these adjustments. The revised designation defines a smaller nonattainment area around the City of Las Vegas and designates the remainder of Clark County with the rest of the State as "unclassifiable/attainment."