Complex sentence: Claims have been made for human presence in the 20,000-30,000 BP timeframe at Pennsylvania's Meadowcroft Rock Shelter and in California's Yuha Desert as well as sites in South America, Central America, and Mesoamerica.
Split into simpler sentences: Claims have been made for human presence during the 20,000-30,000 time frame at Pennsylvania's Meadowcroft Rock Shelter and in California's Yuha Desert. Claims of occupation during the 20,000-30,000 period have also been made regarding sites in South America, Central America, and Mesoamerica.