Between 1850 and 1880, 55,000 Mexican workers immigrated to the United States to become field hands in regions that had, until very recently, belonged to Mexico. The institution of Mexican workers in the United States was well established at this time in commercial agriculture, the mining industry, light industry and the railroad. The working conditions and salaries of the Mexicans were poor.
The presence of Mexican workers in the American labor scene started with the construction of the railroad between Mexico and the U.S. That presence grew between 1880 and 1890. As much as 60 percent of the railway working crews were Mexican.
They were willing to work for low wages.
http://www.pbs.org/kpbs/theborder/history/timeline/17.html
Mexican immigrants mainly settle in "traditional" destination states like California and Texas, which combined are home to well over half of this group. But over the last two decades, the foreign born from Mexico, like other immigrant groups, have begun moving to "nontraditional" settlement areas. These include states in the South, such as Georgia and North Carolina, as well as Midwestern states such as Nebraska and Ohio.
About one of every 10 Mexicans resides in the United States.
http://www.migrationinformation.org/usfocus/display.cfm?ID=767
The first noted trends of Mexican immigration to the United States occurred in the second half of the nineteenth century. Originally, the gold rush in California attracted miners from the Sonoran region of Mexico.
Many Mexicans found work with the railway work force.
The Brazero Program (Mexico Contract Laborer's). The original plan of this program was to form an agreement between Mexico and the United States in which Mexican workers would be sent to places in the United States that needed agricultural labor. Unfortunately, with this system, only a certain number of immigrants were allowed into the U.S.
Immediately after the close of the Brazero program, illegal immigration...