Riches flowed to San Francisco from both the Gold Rush and Nevada’s Comstock Lode, while its natural harbor made it a hub of commerce. Its extensive street grid, presciently laid out in 1847, included a 120–foot wide main stem, Market Street, giving the new city room to grow.

A steam train on Market, opened in 1860, was the first public rail transit, soon supplanted by several horse–drawn street railways. But on the city’s hills, horses struggled, a problem that inspired British mining engineer Andrew Hallidie to adapt his cable ore conveyors to pull rail cars. Hallidie’s Clay Street Hill Railroad, opened in 1873, briefly revolutionized mass transit. Almost 30 US cities including New York, Chicago, Kansas City, Seattle, Los Angeles, and Oakland soon opened cable lines, which were twice as fast as horsecars, even on flat routes. In San Francisco, cable lines proliferated, helping create neighborhoods along Castro, California, Haight, Hayes, and many other streets while cementing Market Street, with its five cable lines, as the core commercial street.

Cable’s national reign was fleeting. In 1887, Frank Sprague’s electric streetcar in Richmond, VA sparked another revolution, again doubling transit speed and creating ‘streetcar suburbs’ out of empty land.

But San Francisco stayed attached to its cables for a combination of physical and political reasons. Five years into the 20th Century, when cable cars were considered obsolete almost everywhere else, they still ruled the roost in San Francisco, so dominant that an entire part of the city, ‘South of the Slot’, was known by its location compared to the cable channel running along Market Street.

This changed on the morning of April 18, 1906.