Hi, my family has the last name Muñoz, which is the original spanish last name and Munos is a variation and misspelling of the first one, after years of bad home schooled people. The last name Munoz is one of the most common in Mexico, and Spain; but there is a huge chance of finding information in the Mexican Census. I will ask my grandfather if he has any family named Dolores Muñoz, he is about 84 but remember 4 generations before him. ;)
Also the name of your great-grandmothers parents will be appreciated, to be more specific.