http://publications.iowa.gov/6465/ RAGBRAI Learn about the Land; Day 2, July 2008 State agencies Recreation and tourism Land use planning On today’s ride we continue riding across the Southern Iowa Drift Plain. This landform region covers over 40% of the state and comprises most of southern Iowa. Over the last several million years Iowa was subjected to at least seven glacial advances. The last of these older advances occurred approximately 500,000 years ago. Since then the landscape has been subjected to stream erosion and from12,500-24,000 years ago was mantled with a thick blanket of loess before being further eroded. 2008-07-21 Departmental Report NonPeerReviewed pdf http://publications.iowa.gov/6465/1/2008day2.pdf (2008) RAGBRAI Learn about the Land; Day 2, July 2008. Natural Resources, Department of. http://publications.iowa.gov/6465/http://publications.iowa.gov/6465/1/