[5] Patrick spent the next five years working on his family farm at Fort Hill and reading extensively in his father's library.

[4] He suffered a severe health breakdown after a year,[7] and went to live on the Arkansas farm of his brother, John C. Calhoun II.

[7] He formed a syndicate of investors in 1886 and won control of the Richmond and West Point Terminal Railway and Warehouse Company.

[9] He was ousted by a similar corporate coup in 1893, but the company went bankrupt two years later and Calhoun acted as an agent for J. P. Morgan in buying the railroad and integrating it into the Southern Railway.

[10] He invested heavily in street railways, directing or reorganizing systems in Baltimore, Maryland; Philadelphia, Pennsylvania; and St. Louis, Missouri.

He now began development of that land into a new planned community for the wealthy and upper classes, and named it Euclid Heights.

He merged the street railways of that city into a single firm, the United Railroads of San Francisco (URR), and became the company president in 1906.

[8] He then gave local political boss Abe Ruef $200,000 ($6,782,222 in 2023 dollars) to allow him to build overhead electric wires to supply his streetcars with power.

[12] Calhoun was indicted and placed on trial several times, but eventually charges against him were dismissed when his political supporters won office.

[14][15] In 1912, an investigation by the California Railway Commission found that Calhoun had concealed a $1.2 million ($40,693,333 in 2023 dollars) loss in his San Francisco company in order to keep the stock price high.