During 1975-6, extensive data were collected on late prehistoric cultures in the Central Rift Valley, Kenya, and adjoining regions. A stratified archeological survey was conducted in an area of about 22,000 km2 centering on the Naivasha and Nakuru lake basins. The area was divided into 20 units (strata) defined by elevation and precipitation, and approximately 5% of each unit was targeted for survey. Although the study was aimed primarily at later stone age cultures, no stage of prehistory was excluded from the survey, and the data also reflect earlier stone age and iron age cultures. Just over 100 sites were located, and test excavations were conducted in 9 of them. A preliminary analysis of the survey materials and excavated data provides interesting insights on settlement behavior, technology, and culture history