Rural Forest Markets Act of 2020 This bill directs the Department of Agriculture (USDA) to establish the Rural Forest Market Investment Program to guarantee investments to finance certain projects that will enable rural private forest landowners to participate in an innovative market for forest carbon or other products. Eligible projects are projects developed by a private entity or a publicly supported, charitable nonprofit organization engaged in the aggregation of sustainable forestry practices implemented by rural private forest landowners to facilitate the sale of credits in the voluntary carbon market or other environmental market using a methodology approved by a credible, third-party entity. USDA may guarantee up to $150 million with respect to each investment. Authority to carry out the program terminates on September 30, 2023.