Every corner of San Francisco has an amazing story to tell. "Portals of the Past" is a rollicking tour through the city's wild history, from the days when Colombian Mammoths roamed North Beach to the Gold Rush delirium, the dot-com madness and beyond. Read "Portals of the Past" every other Saturday in the San Francisco Chronicle, and coming soon, listen to the podcast at portalsofthepastsf.com.