Pueblo IV Era
The Pueblo IV Period (AD 1350 to AD 1600) was the fourth period of ancient pueblo life in the American Southwest. At the end of prior Pueblo III Period, Ancestral Puebloans living in the Colorado and Utah regions abandoned their settlements and migrated south to the Pecos River and Rio Grande valleys. As a result, pueblos in those areas saw a significant increase in total population.
The Pueblo IV Period (Pecos Classification) is similar to the "Regressive Pueblo Period" or, referring to the Ancient Pueblo People of Colorado and Utah, the "Post Pueblo Period."
Puebloan villages in Arizona and New Mexico had multi-storied pueblos of up to a thousand clustered rooms. The New Mexico villages were generally larger than those of western region, which had large plazas with long, rectangular kivas.
The great migration out of Colorado and Utah at the end of the Pueblo III Period resulted in an influx of people into the Rio Grande and Little Colorado River valleys. Within Arizona and New Mexico there was an aggregation of people from outlying sites to larger pueblos. The puebloan territory of the Pueblo IV Period also included the White Mountains, Verde Valley, Anderson Mesa, and Pecos areas.
Taos Pueblo 1880
An upsurge in the lifestyle of the Rio Grande valley residents in the beginning of the Pueblo IV Period was tempered by the 16th century Spanish colonization of the Americas which extended north into New Mexico. Don Juan de Onate, the colonial governor of the New Spain province of New Mexico, led 400 soldiers and farmers in 1598 to establish settlements into the Rio Grande valley area.
...
Wikipedia