State regulators deny accusations that the fines are part of an effort to put small drillers out of business.
Oil and Gas
The USGS said the Mancos Shale formation holds about 66.3 trillion cubic feet of gas, up from 1.6 trillion estimated in 2003.
Around the country, and in Colorado, houses, schools and shopping centers are being built on old oil and gas fields.
As lawmakers start the 2016 session, Colorado's governor lays out his biggest priorities, and faces questions about promises made last year.
Methane is a target for regulators and scientists because of its power to warm the planet.