A peer-reviewed paper about a fossil discovery made right down the highway from where I live has just been published in Science Magazine.
The discovery was made in 2016 by scientists from the Denver Museum of Nature and Science (DMNS) ...
The discovery location is referred to in the paper as the Coral Bluffs Study Area and is located on the edge of the Denver Basin near Colorado Springs, Co. The Denver Basin is a geological structural basin that is approximately centered in eastern Colorado but also extends into Wyoming, Nebraska, and Kansas. The basin first formed as a result of the orogeny (mountain-building event) that created the Ancestral Rocky Mountains, was later inundated and filled with sediment by the Cretaceous Interior Seaway, and during the Laramide orogeny (spanning in time the dinosaur extinction 66 millions years ago), was deepened on the eastern side and further filled with thick sediments eroded from the modern Rocky Mountains.
The discovery is comprised of mammalian and plant fossils that were deposited in mudstones and sandstones that can be accurately dated to soon after (in geologic time) the Chicxulub asteroid impacted Mexico's Yucatan Peninsula, bringing about the extinction of non-avian dinosaurs (the most widely accepted theory of the cause of the dinosaur extinction).
The extensive discovery of plant and animal fossils at Coral Bluffs greatly augments what little fossil evidence had previously been accumulated for this period and provides new insight into the direction of evolution for post-impact plant and animal species, particularly for the rise of mammals that preceded our own species.
All of this is explained in great detail in the paper referenced above. In addition, there are a couple of excellent sources that discuss the discovery at a more nonprofessional level. These include the DMNS's execllent website as well as a program entitled "Rise of the Mammals" streaming on PBS NOVA and soon to be broadcast nationally starting October 30th (check your local listings).