Bladensburg lies in the geologic region known as "Dinosaur Alley." It is the area on the East Coast of the United States were the greatest number of dinosaur bones have been found. Dinosaur Alley runs along the Route 1 corridor between Baltimore and Washington. The layers of earth in this area are about 100 million years old and are made primarily of clay and sand, not rock.
One hundred million years ago, during the middle Cretaceous period, the Baltimore-Washington area was a flat plain near the sea, just as it is today. The climate, however, was warmer. The forests of that time consisted of conifers (pine trees and their relatives), cycad-like plants (conifer relatives that look like palms), and tree ferns. There were no grasses, briers, or oaks; flowering plants had not even developed yet. This was the home of the dinosaur.
During colonial times, iron-rich ore beds were dug by hand from surface pits. Occasionally dinosaur bones and other fossils were found, but the fossils' scientific importance was not understood at the time. The first dinosaur bones were said to have come from "iron mines in Bladensburg," but the actual site was nine miles north at Mulrkirk. These first discoveries (reported by Philip Thomas Tyson, state geologist in November 1858) were the bones and teeth of a large dinosaur named Astrodon johnstoni (Brachiosaur). Astrodon means star-tooth. It ws the first sauropod (a dinosaur with a long neck and a long tail) found in North America. In 1998, the Astrodon became Maryland's official state dinosaur.
At present, about a dozen categories of dinosaurs are known to be from Dinosaur Alley. These finds represent almost all the categories of dinosaurs. Nonetheless, it is generally believed by paleontologists that the fossils that have been found represent fewer than half the dinosaur species that lived in the Bladensburg area. There are many more species and skeletons to be found.