During the very first recorded in-land European exploration of what we now consider California, a Spanish expedition crested a ridge and beheld San Fransisco Bay for the first time. While they did not see it for the hot bit of real estate it would become in the modern day, the site of the discovery is still marked with a large granite monument.
The Portolá Expedition, led by Spanish military man Gaspar de Portolá, was actually in search of Monterey Bay when they happened upon the scenic lookout that revealed (what would come to be known as) San Francisco Bay. The large expedition party had come up north from San Diego, trudging across the inland territory, not really sure how to find the bay they were looking for. On November 1st, 1769, a member of the expedition stumbled upon the large bay, viewing it from a spot on today's Sweeney Ridge. He reported back to the rest of the group, correctly calling the bay an "estuary." Portolá's force continued to explore the area but was finally turned away by hostile Native American tribes, and inhospitable wilderness, returning to San Diego without having discovered the bay they were looking for.
The expedition would eventually locate Monterey Bay, but their accidental discovery of San Francisco Bay still lives on as the first time Europeans laid eyes on the now-famous inlet.
Today, the spot where the explorers first saw the bay is marked with a tall granite monument, and is protected as a National Historic Landmark. Of course the exact place where the expedition discovered the bay is not known, but the monument is placed in a likely spot. Good enough for government work, as they say.