Water. When San Francisco was first becoming a city, it had many more waterways than now. Those were wet years. When dry years came the gullies became annoyances. People filled in the creeks and low areas with sand, debris and gravel. Marshes and sloughs were filled, too. The edges of the city were expanded into the Bay, making sailable water into salable lots. Today's rain goes right into sewers, for the most part. Few absorbent soils are still exposed. Remarkably, surface creeks do still flow, here and there. And when you dig, you still find groundwater. If you search you'll see springs, mostly small, seeping and trickling out onto our landscape.
Land. Look closely. The map shows recognizable cuts where streets were sculpted. Enjoy the seeking, without labels. Get to know your landscape. Find things you didn't realize you were looking for.