PORTLAND, Ore. (AP) — Two of the first states to broadly legalize marijuana took different approaches to regulation that left Oregon with a vast oversupply and Colorado with a well-balanced market. But in both states prices for bud have plummeted.

A new Oregon report by law enforcement found nearly 70 percent of the legal recreational marijuana grown goes unsold, while an unrelated state-commissioned Colorado study found most growers there are planting less than half of their legal allotment — and still meeting demand.

The Oregon study released by the Oregon-Idaho High Intensity Drug Trafficki...