The Bonner Mill passed from ACM to Champion International in 1972 and then to Stimson Lumber in 1993. The mill closed in 2008. Anaconda sold the Bonner mill and its timberlands to US Plywood-Champion Papers, Inc. in 1972, ending the almost continuous ownership of the Anaconda Company.

By 1974, US Plywood-Champion Papers, Inc. had become Champion International and was in the business of making plywood. The Bonner Mill however, was not set up for plywood operations. The Company immediately began construction of a plywood mill. The first plywood was produced in December 1973 from one of the largest plywood plants in the country. The mill continued to be called the Anaconda Mill into the 1980s.

Plywood pushed the production of the mill dramatically. Champion brought in workers with experience from other mills. By 1976, there were over 1,000 workers at the mill with a payroll of $1,248,000. Champion then bought the Hoerner-Waldorf Company in 1977, which made them the owner of the Frenchtown pulp and linerboard plant.

Unlike Anaconda, which Champion described as a “custodial type of manager,” Champion did not intend to be there forever. In a 1978 draft report, the Champion stated, "It is anticipated this first operating plan [for Montana Forest lands] will be for a period of 18 years. During this period, the remaining old growth timber will be removed."

Champion carried out this plan and with just 2.4 billion feet of Anaconda’s vast timberlands left to cut; it was time to get out. In 1993, Champion sold its 867,000 acres of timberlands to Plum Creek Corporation and its mill to Oregon-based Stimson Lumber Company.

Under Stimson, the Bonner plant continued to produce plywood, studs, and premium lumber. They obtained a 10-year contract from Plum Creek to supply the Bonner and Libby mills with 100,000 board feet of timber per year as part of the settlement. However the mills needed twice as much raw material to operate at previous levels. At the end of the 10-year contract, Stimson was forced to look for timberlands to harvest, generally private lands as there was little lumber offered by the National Forests at that time.

Ironically, on August 3, 2005, the Missoulian announced both that the Milltown Dam Consent Degree had been filed with the Department of Justice and also that the Stimson Mill was cutting 120 jobs and ending the production of commodity plywood. The mill's work force was cut to 330. Additional cuts were made in 2007 and, as of 2008, the mill was indefinitely closed. The contents on the mill were auctioned off and the future awaited a new buyer, ending an era of 122 years of continuous lumber production, most of which was under the Anaconda Company.

New mill owner Mike Boehme, Commissioner Jean Curtiss, and owner Steve Nelson announce the mill purchase in December, 2011. A welcome Missoulian headline greeted readers on December 16, 2011: "New owners take over Stimson's Bonner millsite."

Signs of a new way of life stirred at the mill property with the announcement that Bonner Property Development LLC owned by Steve Nelson and Mike Boehme had purchased the mill site. The mill was to be subdivided into industrial condominiums. Northwest Paint was already operating at the site and in short order several more business start ups were announced. The same day they signed the closing papers Bonner Property Development LLC announced that Willis Enterprises and Boise Inc. had an agreement start a chipping operation at the site. Willis has since expanded its operationsand consturcted a permanent chipper on land its purchased from Bonner Property Development LLC.

In November, 2012 the Aluminum Co. of Maine Inc. signed a leased to establish a 70,000-square-foot aluminum trailer manufacturing facility inside the plywood building on the site. Other new tenants include Hellgate Forge and MontanaGrow, a startup natural fertilizer company.

In addition to purchasing the mill property, Boehme and Nelson also purchased the Bonner houses on both sides of the highway with the intent of restoring and renting them.

Environmental concerns plagued the millsite and the Stimson Lumber Company was required to clean up significant PCB contamination.