The Jefferson County Sheriff's Office and the West Metro Drug Task Force seized more than 5,100 marijuana plants weighing nearly 2,000 pounds from land near Sugarloaf Mountain on July 9.
The plants have an estimated street value of $2.5 million.
The large grow area had a sophisticated irrigation system using water from a nearby stream, according to sheriff's spokeswoman Jacki Kelley.
"This looked like a very sophisticated operation," Kelley said.
Sugarloaf Mountain is in the Pike National Forest near Cheesman Reservoir.
A horseback rider trying to collect stray cattle stumbled on the plants and contacted the sheriff's office.
It took nearly two days and more than 20 sheriff’s and task force investigators to get to the location and collect all the plants. They were assisted by a UH-60 Black Hawk helicopter flown by the Colorado Air National Guard to lift large bundles of plants out of the steep and rugged terrain. The plants were then loaded onto trucks and taken into evidence.
No suspects were found in the area, but investigators believe several people were living on the land in a makeshift home, which contained food, clothing, sleeping bags, cooking utensils and other household items.
The sheriff's office is asking anyone with information in the case to contact the Jeffco sheriff's tip line at 303-271-5612.