The story of Juan Seguin is illustrative of the history of Spanish speaking Texans of the time.

http://en.wikipedia.org/wiki/Juan_Segu%C3%ADn

Most Texans, Spanish speaking and English speaking, were united in their opposition to the Mexican government, and fought side by side for independence. After independence, there was a wave of English speaking immigrants, and many Spanish speaking Texans found themselves mistrusted and marginalized, leading to a decline in their numbers as many moved south to Mexico.

This isn't quite the same thing that you're asking, but the Treaty of Guadalupe Hidalgo, which ended the war between Mexico and the US, says this:

Mexicans now established in territories previously belonging to Mexico, and which remain for the future within the limits of the United States, as defined by the present treaty, shall be free to continue where they now reside, or to remove at any time to the Mexican republic, retaining the property which they possess in the said territories, or disposing thereof, and removing the proceeds wherever they please, without their being subjected, on this account, to any contribution, tax, or charge whatever.

Those who shall prefer to remain in the said territories, may either retain the title and rights of Mexican citizens, or acquire those of citizens of the United States.

California still occasionally has court cases involving water rights which are decided by reference to Mexican water law.