The Environmental Protection Agency (EPA) is proposing to approve a revision to the Great Basin Unified Air Pollution Control District (GBUAPCD or ``District'') portion of the California State Implementation Plan (SIP). In this action, we are proposing to approve one rule governing the issuance of permits for new and modified major sources in nonattainment areas under part D of title I of the Clean Air Act (CAA or ``the Act'') in the District. We are also proposing to find that PM<INF>10</INF> precursors are not significant contributors to PM<INF>10</INF> levels in the Mono Basin, as the majority of direct PM emissions come from dry lake beds. We are taking comments on this proposal and a final action will follow.