What have I found here?

Asked November 9, 2019, 2:23 PM EST

Greetings, I found this rock specimen on a 8,000 foot elevation mountain near Midwest, Wyoming. These rocks of all sizes were everywhere. It appears that this is lava on the top with limestone under the lava. I would like to explain what this is and how it developed to my grand daughter. Thank you for your time, Gene Anderson


1 Response

Hi, Gene - These actually seem to be sedimentary concretions, rather than basalt. The geology map for the area shows rocks of Cretaceous age, generally shales and sandstones.https://uwdigital.uwyo.edu/islandora/object/wyu%3A2156
It fits with the geology story for that time period when shallow warm seas covered the area. The roadside geology series is good for overall explanations of the state's geology. I suggest looking for a book on Wyoming geology. Your state has a rich history. These are cool fossils.
Have fun exploring with your grand daughter!