The Mother's Day Quarry (MDQ) is a Late Jurassic (Kimmeridgian) fossil site in the Morrison Formation that is located at the base of the Pryor Mountains in Carbon County, Montana. The site was first discovered by the Museum of the Rockies in 1994 and has produced over 2,500 elements since its discovery. Apart from approximately 12 theropod teeth, stegosaur limb material, and two conchostracans found at the site, these elements almost exclusively belong to specimens of the sauropod dinosaur Diplodocus sp. This deposit of fossils is thought to be the result of an age-segregated herd of these dinosaurs congregating at a limited water source and eventually succumbing to drought conditions.