It looks like the Southern E-W band roughly follows I-20, which would tend to hit the major cities there. The patch in Texas runs from Brownsville to Laredo and further NW along the Rio Grande, which I think is a heavily hispanic area - as I've read. the pattern picks up all along the border with Mexico - around El Paso and in Arizona and New Mexico as well. It also corresponds to the poorest area of TX - see http://www.bidc.state.tx.us/maps/TX-PerCapitaIncome.htm for more info.