Timothy Mahon and his brother came to San Rafael from Canada in 1850. Timothy bought a large portion of the land between Fourth and Fifth Streets, between C and D, from the Timothy “Don Timoteo” Murphy estate, including the original adobe used for many years as the county courthouse, which he donated to the county in 1857. In 1875, Timothy Mahon built the Mahon House, an elegant hotel in the French Empire style. It boasted an impressive dining room and was one of the grand hotels of San Rafael.

The Mahon House soon earned the name "Casa Grande" as it was considered San Rafael's most luxurious hotel. An 1876 Marin Journal article described the 40-room hotel as a "superior building" with "large and elegant rooms that had stationary washstands, water and gas, fireplaces and bells" to call Mr. Mahon so that he could "render the stay of his numerous guests comfortably by attending to all their wants."

One of the first retail businesses at the street level was a drug store run by Dr. John C. Wolfe. Wolfe bought land at the south end of D Street, and built a large two-story house there. As early as 1892, the steep road over the hills between San Rafael and Kentfield was called "Wolfe Grade."