The Allen coal mine was established in 1950, however the planning for the mine preceded the second world war. In 1940 a project for locating potential coal sites was conducted under the name "Apache Project". The bituminous coal found in the location of the future Allen Mine was found to be of particularly useful for coking coal. The coal seam was found to be five and a half feet to six feet thick, and estimated to contain around eighty million tons of coal. In 1950 CF&I contracted the Utah construction co. to develop the western and eastern portal slop entries. They were also contracted to open up a four-hundred foot ventilation shaft for the mine.

Development of the Mine was completed through the Utah Construction company by August of 1951 when CF&I took over operations of the site. The mine was named Allen after Charles Allen Jr. whom had taken control of CF&I from the Rockefeller interests in 1945. The Allen mine was considered one of the most advanced mechanized mining operations when it first opened while employing around five hundred people. The eastern slope entrance had a forty eight inch wide conveyor belt to bringing out around 700 tons of coal per hour. The conveyor belt brought the coal to a tipple and coal breaker and coal loading facilities for rail road cars. The western portal however operated through a rope hoist and car system. The rope haulage and car system led to a loading tipple for rail cars for transport.

All mining done until the early 1970's was done by conventional room and pillar mining system. Coal removal revolved around steel beams, props, roof bolts, plates as well as netting. Continuous miners, coal cutters, shuttle cars, and thirty inch panel belts were utilized. The coal was then loaded into a forty eight inch track gauge bottom dump rail cars pulled by electric locomotive.

In the 1970's two concrete twelve thousand ton, one hundred and eighty six feet high, silos were constructed at the Eastern portal. The silos were filled to load sixty train cars. These rail cars were taken from the Allen mine to Jansen and then transported to Pueblo. In addition there was two hundred and thirty ton underground facility consisting storage and surge bins for the coal. Also underground there was a one hundred ton rock bin so that mine rock could be sorted apart from the coal.

By the early 1970's a proposal was made to start a longwall system using a five hundred ton hydraulic roof supports and mining four hundred and fifty foot panels. Initially the system offered a myriad of problems, but eventually provided a substantial portion of production. Each pass of the longwall shearer a thirty inch cut was made in two stages, one upper and one lower. Approximately three hundred and fifty tons of coal were mined per pass with the coal removed by chain conveyor to a panel belt and train haulage.

The Allen mine was sold along with the Maxwell mine to the Wyoming Fuel company for a reported forty million dollars effective by December 16, 1983. By the time twenty six million fifty five thousand and four hundred and twenty two tons of coal had been mined.