You're right, there is a lot more talk about it in the past month.
Good that people are becoming more aware of it and it must shock them, the way it did me a couple of years ago, when I was first learning some of this stuff.
The Treaty of Guadalupe Hidalgo was the peace treaty that ended the Mexican-American War (18461848). The treaty provided for the Mexican Cession, in which Mexico ceded 1.36 million km² (525,000 square miles) to the United States in exchange for USD$15 million. The United States also agreed to take over $3.25 million in debts Mexico owed to American citizens.
The cession included parts of the modern-day U.S. states of Colorado, Arizona, New Mexico, and Wyoming, as well as the whole of California, Nevada, and Utah. The remaining parts of what are today the states of Arizona and New Mexico were later ceded under the 1853 Gadsden Purchase.
The treaty was signed by Nicholas P. Trist on behalf of the United States and three plenipotentiary representatives of Mexico on February 2, 1848, at the Villa of Guadalupe (today Gustavo A. Madero, D.F.), slightly north of Mexico City. It was subsequently ratified by the United States Senate on March 10 and by the Mexican government on May 19; the countries' ratifications were duly exchanged on May 30, 1848, at the city of Santiago de Querétaro.