Temple created a thriving cattle ranch and prospered, becoming after Abel Stearns, the wealthiest man in post-statehood Los Angeles County.

During the 1840s, Temple was active in ship-bound trade throughout the coasts of Alta California and central Mexico, and owned extensive lands between Acapulco and Mazatlán.

In 1856, by providing, through his son-in-law, Gregorio de Ajuria (1819–1861), the funds to finance the Plan of Ayutla removing Antonio López de Santa Anna as Mexico's president/dictator, he became the lessor of the Mexican national mint, a concession held by him and his daughter until 1893, when the mint was nationalized by Porfirio Díaz.

The ill-fated timing of his construction projects in late 1850s Los Angeles, which was in an economic downturn, was exacerbated by a flood in 1861-62 and drought from 1862 to 1865 that almost destroyed the cattle industry, then the backbone of the local economy.

Juan Temple lived his last years in San Francisco where he died in 1866, two months after selling Rancho Los Cerritos to Flint, Bixby & Co for $20,000, or less than a dollar an acre, during a prolonged depressed real estate market.