Alliance Defending Freedom, a Christian legal advocacy group that filed the lawsuit on behalf of Snelling, alleged discrimination by the park. “National Park Service: Research in Grand Canyon okay for geologists … but not Christian ones,” read the headline on their press release. (Interior department and NPS spokespeople declined to comment because of the pending litigation.)

If the permit application hit a nerve, it’s because young-Earth creationists have a bit of an obsession with the Grand Canyon. Where geologists see billions of years of rock layers carved out by a persistent flow of water, young-Earth creationists see sediments laid down in Noah’s flood. As the flood receded, they believe, water became trapped behind natural dams, until it finally broke through in a “catastrophic erosion” that carved the Grand Canyon.

This is the story told on religious rafting trips organized by companies like Canyon Ministries, for which Snelling also works as a guide. In 2004, a book by the Canyon Ministries founder Tom Vail caused a stir when it was sold at the national park’s bookstores.

It’s all part of an uneasy relationship between the park and young-Earth creationists. The park does permit the rafting trips, and it has allowed creationists, including Snelling according to the lawsuit, to work in the park before. Another prominent young-Earth creationist, Steve Austin, took photos of nautiloid fossils in the park and used them to argue that the creatures died during the flood. “I think the NPS has felt a bit stung by past creationist research in the Grand Canyon,” says Steven Newton, who teaches geology at College of Marin and serves as the programs and policy director for the National Center for Science Education, a nonprofit that opposes teaching creationism in public schools.

Exactly why the park did not grant Snelling’s application is, of course, now the subject of a lawsuit. His project did involve collecting a sizable number of rocks, which can invite more scrutiny. In an email to Snelling filed as part of the lawsuit, a park officer said the project was not granted because the type of rock he wanted to study can also be found outside of the Grand Canyon. The park solicited peer reviews from three mainstream geologists. One mentioned the rocks could be found elsewhere; all three overwhelmingly denounced the work as not scientifically valid, a criterion the park also uses to evaluate proposals. Snelling, who holds a Ph.D. in geology, did not disclose his Answers in Genesis affiliation, nor did he explicitly say he wanted to prove the Grand Canyon is young in his initial permit application, but the reviewers became aware of his reputation.

Geology as a profession has struggled with what to do with young-Earth creationists, whose beliefs are contradicted by literal mountains of scientific evidence. Shut them down, and you get cries of censorship—like this lawsuit. “This just so plays into their hands,” Newton says about the national park’s treatment of Snelling’s application. Newton favors letting creationists do their research and then arguing on the merits of their science. But allowing them to present at scientific conferences, others say, is lending creationists legitimacy.