An expert on the Late Jurassic, he has spent more than twenty-five years excavating fossils across the western United States, authoring and coauthoring more than 55 professional papers, ranging from Triassic to Cretaceous, with a few Cambrian and Cenozoic studies appearing as well.

In addition to dinosaurs, he has spent over a decade working in the Cambrian shales of the western United States.

Gay of Colorado Canyons Association formally published their study on the oldest known dinosaur from Utah, a neotheropod that is likely an animal similar to Coelophysis.

[4] His researches in the Late Jurassic of the Colorado Plateau and Rocky Mountains includes the geographic and environmental distributions of microvertebrates and dinosaurs.

Foster had a ceratosaurid ceratosaur theropod dinosaur, Fosterovenator, named after him in 2014[5] His researches in the Cambrian of the Great Basin and Colorado Plateau, includes the study of taphonomy and biostratinomy of trilobites, and what this information indicates about the paleoenvironmental conditions on the shallow shelf of western North American during the early Paleozoic.