CalEnviroScreen (CES) is a screening tool developed by the California Environmental Protection Agency that scores California census tracts based on measurements of pollution burden and population vulnerability, in order to direct resources toward improving public health in disadvantaged and burdened communities. Communities near the U.S.-Mexico border face pollution burdens from sources in Baja California that are not fully incorporated into CalEnviroScreen. To improve the understanding of impacts of air pollution from Mexico on border communities and provide critical data to the California Air Resources Board, we carried out three types of analysis. The first was mapping activities for sources in Baja California, including burn events; the second was modeling the potential areas of influence (PAIs) of selected sources and potential source regions (PSRs) for California communities; and the third was to estimate the impact of sources close to the border on existing community scores in the Environmental Justice Screening Model (EJSM). A systematic methodology was developed that included satellite imagery and ground-based verification of locations of sources, and a database that contains 1174 facilities was created for use in this and future projects. Modeling results strongly suggest that areas in the US immediately adjacent to the border and farther north in San Diego County are likely to be affected by emission sources in the Mexican side, not only by within a 1.5-km buffer of the border but also from potential regions both inland and off-shore within a 50-km buffer. A pilot method was developed for measuring and mapping fire activity near the US-Mexico border, and we present mapped locations and temporal patterns of agricultural burning on both sides of the border. Data also indicated that urban burning was common in Mexicali. Air toxics emissions sources in Mexico have a clear potential to affect communities and individuals in the US-Mexico border region. Recommendations include using the tools developed in this analysis to determine border-specific approaches to improving CES that take into account Baja California sources.