Marking the past
Few underwater impact structures this old survive today; that's because oceanic crust, where the crater lies, is constantly reworked. But this ancient, shallow carbonate shelf similar to today's Bahamas managed to endure several cycles of mountain building along western North America.
Geologists first assembled these clues in the 1990s, announcing discovery of the crater in 1997. Now, Retzler and his co-authors at Idaho State University have painstakingly mapped the thickness and position of different rock layers within the crater to precisely determine its size and shape