It was not until 1924 that all Native Americans became US citizens. Prior to that they first had to give up tribal affiliation to gain US citizenship.
https://en.wikipedia.org/wiki/Mission_Indians
“Spanish explorers arrived on California's coasts as early as the mid-16th century. In 1769 the first Spanish Franciscan mission was built in San Diego. Local tribes were relocated and conscripted into forced labor on the mission, stretching from San Diego to San Francisco. Disease, starvation, over work and torture decimated these tribes.”