Passport data for Mexico's Guanajuato State were used to locate the sites where maize was collected in the 1940s and 1950s in an effort to document and conserve diversity. A map presenting survey points illustrates that collections have occurred repeatedly in the same locations. Observations of these locations reveal that urbanization and industrialization, not high yielding varieties, are displacing traditional varieties. Non-linear principal components analysis was used to assess associations between variables in areas where maize persists. Landraces appear to be associated with mountains and mesas, mixed cropping, little or no access to irrigation and areas classified as having low agricultural capacity; conversely, landraces have more commonly been replaced in areas of high agricultural capacity. The areas of high agriculture capacity, located in the riparian areas and plains, also have been the easiest to develop for urban and industrial use. Increasingly high rates of urbanization and development in areas of high agriculture capacity will impede the conservation of crop diversity in these areas.