Asteroid impacts belong in this thread, right?
I wonder how many people have gone over/around these craters without knowing what they were. Pretty cool find, and it would be really cool if they could find the main impact source.
Secondary Cratering Discovered on Earth: The Wyoming Impact Crater Field
Several dozen small impact craters, 10–70-m in size, have been discovered in southeastern Wyoming.
A team of U.S. and German geoscientists found these ancient craters in exposed sedimentary layers from the Permian period (280 million years ago). After discovering the first craters, the team initially suspected that they are a crater-strewn field, formed by the breakup of an asteroid that entered the atmosphere. However, with the discovery of more and more craters over a wide area, this interpretation was ruled out.
Many of the craters are clustered in groups and are aligned along rays. Furthermore, several craters are elliptical, allowing the reconstruction of the incoming paths of the impactors. The reconstructed trajectories have a radial pattern.
“The trajectories indicate a single source and show that the craters were formed by ejected blocks from a large primary crater,” said project leader Thomas Kenkmann, professor of geology at the University of Freiburg, Germany. “Secondary craters around larger craters are well known from other planets and moons but have never been found on Earth.”
Here's a PDF with some more info.