The Environmental Protection Agency (EPA) is finalizing a determination that the Nevada County (Western part) and Ventura County areas in California, both classified as Serious for the 2008 ozone National Ambient Air Quality Standards (NAAQS), attained the 2008 ozone NAAQS by the July 20, 2021 attainment date. The EPA is also finalizing a determination that six areas in California classified as Marginal for the 2015 ozone NAAQS, attained the 2015 ozone NAAQS by the August 3, 2021 attainment date. These six areas are: Butte County, Calaveras County, San Luis Obispo (Eastern part), Sutter Buttes, Tuolumne County, and Tuscan Buttes. Our final determination of attainment is based on the exclusion of exceedances of the 2008 and 2015 ozone NAAQS that occurred on multiple days in 2018 and 2020, because the exceedances were due to exceptional events. We are also finalizing our determination that the requirement for the State to have contingency measures for Reasonable Further Progress (RFP) and attainment for the 2008 ozone NAAQS for the Nevada County (Western part) and Ventura nonattainment areas will no longer apply, because the contingency measures will never be needed given the attainment of the NAAQS by the attainment date. This action fulfills the EPA's statutory obligation to determine whether these ozone nonattainment areas attained the NAAQS by the relevant attainment dates.