sentences:  The provisional government's first legislature met on December 6, 1847, beginning American civil government in the region.The Mexican–American War ended February 3, 1848, with Mora Valley and rest of the region then under formal US control, as the Mexican Cession of the Treaty of Guadalupe Hidalgo relinquished all claims by Mexico to lands north of the Rio Grande.Still claimed by state of Texas until the Compromise of 1850, the New Mexico Territory, with smaller boundaries, was formalized on September 9 of that year.