1. The Maquoketa Formation (Upper Ordovician) in Iowa [cartographic material] Yale Public content 1971. 2018-04-20T18:43:31Z. 2021-05-04T22:29:48Z. Parker, Mary Combs. Iowa Geological Survey. English. cartographic image. Public. Iowa and Iowa. Ordovician and From 425 to 500 million years ago.