In 1874 Cope discovered the Puerco formation in New Mexico during the Wheeler Survey. The Puerco formation was a layer of soft rock 500 feet thick along the upper Puerco River near Cuba, New Mexico. It was green and black marl (that contained chemicals used in making fertilizer). Fossils were later found by someone at a similar formation west of there in a different county. Cope said it was like those fossils came from his Puerco formation, which he discovered. His cliff may have been dug by the river over a long time and it looked like it had been there a long time. It was something the scientists he knew had not seen before him. As part of the Wheeler Survey, he was able to shop at commissaries. He was able to get his finding in the reports the survey published. He brought his wife and daughter along on one trip of the survey, renting a house for them. As a volunteer, he paid his own way.