The recovery of nearly 250 burials at the El Olivar site provided the opportunity to address questions regarding the groups inhabited coastal settings of the semiarid north of Chile between the 800 and 1540 AD. Stable isotopes of carbon, nitrogen, and oxygen were analyzed from 60 human samples. Radiocarbon (14C) analyses were conducted in 20 samples from camelids and 42 human samples. Subsequently, a sample of 25 individuals exhibiting diagnostic cultural features of the Las & Aacute;nimas Cultural Complex (LACC) and the Chilean Diaguita Culture (CDC) was selected for the purpose of assessing differences in their diet and mobility and clarifying their chronology. The delta 13C and delta 15N values obtained revealed the existence of a small group of individuals (n=6) with a diet based on C3 plants and terrestrial protein, and another major group (n=33) with values compatible with the consumption of C4 plants and marine resources. Four of the six individuals of the small group presented & Aacute;nimas diagnostic features, and in the major group were identified both & Aacute;nimas and Diaguita individuals. The delta 18O values exhibited a similarity between the & Aacute;nimas and Diaguita individuals, suggesting coastal-to-inland mobility in both groups. Calibrated 14C dates indicate that El Olivar was occupied for a period of nearly 380 years, spanning between 1150 and 1536 AD, and that between the 1300 and 1400 AD, & Aacute;nimas and Diaguita individuals coexisted at El Olivar. These findings call into question the current thought that the CDC emerged from the LACC around 1000 AD, and that both represent different archaeological entities.