The Army has found feral hemp, also known as ditch weed, at Rocky Mountain Arsenal north of Denver.
The army has been reseeding parts of the arsenal as part of its cleanup work there.
Denver media reports that when the seed started to grow, marijuana popped up, though the plants aren't commercial-grade marijuana.
The Army blames a supplier for the ditch weed.
The Army says it bought mulch for its ground cover from a place in Kansas, where the low-grade weed is common.