Grandview Park, which locals also call Turtle Hill, is a small hilltop park in the Sunset District. SF Rec and Park lists it at Moraga Street and 14th Avenue. Wikipedia says it covers 3.98 acres and its summit rises to about 666 feet.
Rock from the sea floor
The hill is made of Franciscan chert that's 140 million years old, according to Rec and Park. The rock formed on the ancient sea floor from the silica shells of tiny radiolaria mixed with dust blown from inland deserts. It was later lifted onto land.
Rare plants
Wikipedia says the park is one of the last places in the city for several native plants, including the endangered Franciscan wallflower and dune tansy. Rec and Park explains that development has cut off the supply of wind-blown sand, so eroded sand doesn't come back. That's why visitors are asked to stay on stairways and paths.
Getting to the top
The trail is about 0.2 miles, and most of the climb is wooden stairs. A short loop around the top is on soft, sandy soil. Wikipedia notes that the 16th Avenue Tiled Steps also lead up to the park. Rec and Park says views stretch from downtown and Golden Gate Park to Point Reyes and Lake Merced.