By the age of twenty-one, Reamer had moved to San Diego and had opened the architectural office of Zimmer & Reamer in partnership with Samuel B. Zimmer. The firm produced a wide variety of projects, but the only surviving example of Zimmer & Reamer's work is the George H. Hill Block in the Gaslamp District. The partnership dissolved in 1898, but Reamer continued to work on his own, including work at the Hotel del Coronado. During this period he became acquainted with the president of the Yellowstone Park Company, Harry W. Child.