While Monnette was trained as an attorney, his father's foray into mining in 1904–1906 changed his career path. In 1906, the elder Monnette struck a significant gold vein in the previously thought tapped out Mohawk Mine,
Tonopah, Nevada (near
Goldfield, Nevada). The strike, known as the Monnette-Hayes Lease, with mining expert G. H. Hayes, set records for the value of the ore shipped in 1906. Eventually, Mervin Monnette realized a $5,000,000 profit on the Mohawk, which he assigned to his son for investment. With his father's mining proceeds, Orra Monnette began purchasing stock in Los Angeles area banks. Eventually, this led to a controlling interest in the American National Bank of Los Angeles (ANB). In 1909, ANB was merged into Citizens Trust and Savings Bank of Los Angeles. In 1911, Monnette purchased the Broadway Bank and Trust Company, which when merged with the family's other holdings formed the Citizens Bank and Trust Company, of which Orra E. Monnette was chairman of the board. Monnette left Citizens in 1922. His next venture, opening at the corner of Wilshire and Western Avenues in Los Angeles in 1923 was christened
Bank of America, Los Angeles (BoA). On opening day, the bank posted an operating capital of one million dollars. Monnette's intention was to build capital for national expansion; however, over the course of the 1920s, Bank of Italy's
Amadeo Giannini began buying stock in BoA, L.A. In 1928 Monnette and Giannini, agreed that a merger of both entities under the Bank of America name promised the best opportunity for all concerned. As part of the deal, Monnette sold his rights to the "Foundation Story" of the combined entity. Monnette was growing concerned about the stock and financial markets. The formal name change to
Bank of America National Trust and Savings Bank. Initially, Monnette was named co-chairman of the new BoA and made a director of the bank. During the early 1930s, with his interests elsewhere, Monnette was made a vice president in the bank and retained his board seat. Monnette also founded the Lincoln Mortgage Company of California, which was not included in the BoA merger. Monnette retained control of the company and continued to serve as its president until his death. ==Civic life==