ISBN: | 978-5-5120-8274-4 |
High Quality Content by WIKIPEDIA articles! The Pre-Illinoian Stage is often synonymous with Pre-Illinoian glacial and used by Quaternary geologists for the early and middle Pleistocene glacial and interglacial periods of geologic time in North America from ~2.5 Ma—500,000 years ago, a period of ~2 million years.