A reconnaissance flight near Arizona City led to the discovery and raid of a suspected drug cartel scout campsite, one of two such busts in the past few weeks.

Agents with the Border Patrol’s tactical unit then “fast-roped” from a Black Hawk helicopter onto a mountaintop in the Silver Bell mountain range northwest of Tucson, U.S. Customs and Border Protection said Wednesday.

After a foot chase that ended about 30 feet from a cliff with a “dangerous and potentially fatal drop to jagged rocks below,” agents arrested the two suspected scouts who were working out of a mountainside cave on May 20. Cartel scouts are tasked with guiding drug and human smugglers from the border to their next destination. In many cases, they spend weeks at observation posts on hilltops or mountainsides.

The raid resulted in one suspect facing federal criminal charges and the seizure of “a large cache of counter-surveillance equipment,” CBP said in Wednesday’s news release.