In San Mateo County, California, a walker along a creek paused at what seemed an oddly shaped rock and uncovered instead a ten-thousand-year-old mastodon tooth — a remnant of the Pleistocene epoch preserved in remarkable condition beneath the modern Bay Area. The discovery reminds us that the deep past is never fully sealed away; it waits in streambeds and ordinary moments, surfacing when someone chooses to look twice. What the Ice Age left behind, the creek quietly kept.