Online Lecture: The Rock Elm Meteor Impact Structure: Discovery & Basic Geology

Presenter: Bill Cordua, Ph.D., Geology Emeritus, University of Wisconsin River Falls
Link to Presenter: [Bill Cordua's page on Mindat.org](https://www.mindat.org/user-32096.html)
2nd Link to Presenter: Bill Cordua's page at UWRF

Full Title of Lecture: The Rock Elm Meteor Impact Structure, Pierce County, WI: Discovery and Basic Geology

Summary: The Rock Elm structure has been recognized as a geological anomaly for well over a century, attracting prospectors, charlatans and scientists. It is interpreted as formed by an extraterrestrial impact during the middle Ordovician 430-505 Ma. Both gold and diamonds are found in unusual quantities in the alluvium of streams draining the feature. The talk will outline its basic geological features, review the evidence for its interpretation as an impact structure, speculate why gold and diamonds are associated with it and relate it to similar features in the Midwest.

This lecture will be recorded for GSM's YouTube Channel.

Biography: Dr. Bill Cordua is a retired professor from the University of Wisconsin – River Falls where he taught geology for 40 years. He has published many technical articles and written over 100 articles for the general public on geology. Dr. Cordua is in the education division of the Rockhound and Lapidary Hall of Fame and has received the Katherine Greacen Nelson Award honoring those who have made outstanding contributions to the earth sciences in Wisconsin.

Online Lecture Registration Info: Online lectures require free registration for those who are not dues-paying GSM members; dues-paying GSM members receive an e-mail with the link and participation instructions. If you are not a dues-paying member of GSM and wish to attend this free lecture online, register by 8 AM CT Monday, Nov. 24, 2025 by following the registration instructions posted on this lecture's page of GSM's website.

General Info: GSM lectures/seminars with slide show presentations are free and open to the public. They are presented by leading professionals in their fields and are aimed at learners from high school to adult. A question-and-answer session follows each lecture, and these events are eligible for 1 hour of Continuing Education Unit (CEU) credit.

Our full schedule of lectures and labs is posted at GSM's Current Year Schedule, and a printable version is available at GSM's Current Year Schedule (pdf).

Our schedule is planned over 6 months in advance, so changes may occur. Always check GSM’s home page shortly before each lecture for the latest seminar information.