In the middle of the slide sits Nobby Clark's Folly mansion at the intersection of Douglass Street and Caselli Avenue. Douglass Street goes at an angle from the lower left to the upper right and Caselli Avenue goes to the right. The main hill on the left side near the middle is Castro Hill, and then a gap before the lower slopes of Twin Peaks. Eureka Street, which is the first street to the left of Douglass Street, occupies the gap between Castro Hill on the left and the lower slopes of Twin Peaks on the right. Thus there is a Eureka Valley, with Eureka Street as its spine. The other Eureka Valley has a spine along 18th Street.
