While firefighters were battling the Waldo Canyon fire in late June, they stumbled upon an unexpected find -- a 22-acre marijuana grow hidden in public lands.

Steve Segin, a U.S. Forest Service spokesman said there were an estimated 7,500 plants at the site, a living structure and irrigation lines. The area was also sprayed with pesticides. Those plants would bring a street value of $15 million, he said.

Segin said the grow was spotted by a helicopter pilot fighting the fire about a mile from Rampart Range Road.

“A lot of illegal cultivation areas are not that far from developed areas or roads, that’s how they are resupplied,” he said. “They are just far enough off the beaten path to keep from being spotted.”

Most of the plants from the grow were destroyed by the fire and the rest were dug up by forest service employees and later destroyed.

Since 2009, 16 illegal marijuana grows have been raided on public lands in Colorado, according to U.S. Attorney John Walsh.

Segin said most public lands are safe, but people should keep an eye out. If they spot anything suspicious including the marijuana, a living structure or irrigation, they should report it to authorities immediately.

“Just make a note of where you are and leave.”