A 60-foot fault-polished slab over a Corona Heights playground is one of the only outdoor climbing spots inside San Francisco — and the site of a quiet 2014 access fight that traded a city permit for a leave-no-trace pledge.

On Beaver Street — a two-block pitch of pavement that climbs from Castro Street toward Corona Heights, a few doors up from the Castro Theatre — a roughly 60-foot slab of rock leans over a public playground, streaked in diagonal bands of red and tan. Its face is glassy, almost slippery-looking. According to the sign bolted to its base, it was polished that way by millions of years of movement along a fault.

The rock is a slickenside: a surface ground smooth where two sides of a fault slid past each other, the friction generating heat and a fine dust that lubricates and glazes the stone. Geologists from UC Santa Cruz who studied this outcrop (Kirkpatrick et al., published in Geology in 2013) found the polished chert coated in a silica gel a millimeter or two thick. The city's signage goes further, calling it one of the largest exposed slickensides in the world — a popular claim the peer-reviewed work doesn't try to rank, but a striking one to find towering over a jungle gym.

For a rock this unusual, it is also plainly useful: one of only a handful of outdoor climbing spots inside city limits, mostly worked as a top-rope. That combination set up a small municipal fight. In 2014 the Recreation and Parks Department closed the wall — along with Glen Canyon — over worries about damage, and imposed a climbing permit. Climbers organized. The Bay Area Climbers Coalition, then barely a year old, negotiated the permit away in exchange for a leave-no-trace agreement that bars anyone from altering the rock or placing fixed bolts. The permit sign still stands; the city has since said it isn't enforced.

The wall has had harder problems than paperwork. A rockfall over the winter of 2022–23 shut the area for more than a year and a half; it reopened in late 2024 behind a barrier that permanently blocks one route, and a street-facing section stays off-limits after neighbors complained about rock landing on parked cars.

Beaver Street feeds a much older Bay Area habit of learning to climb on city rock. Across the bay, at Indian Rock Park in the Berkeley hills — volcanic boulders long significant to Ohlone people — climbers have trained since the 1930s. John Sherman, who got hooked there as a teenager in the 1970s, went on to invent the V-scale that grades boulder problems worldwide.

Today, past the playground, the whole record is still there for anyone with a rope and a bag of chalk: a wall a fault rubbed smooth, a permit sign nobody checks, and a barrier marking where the hill let go.