On Mariposa Street, just east of Potrero Avenue. This one-block slope is at the beginning of my Friday evening walk from KQED to the Ferry Building. From that stop sign up above, I turn right, then cross U.S. 101 on the pedestrian overpass that connects to 18th Street on the east side of the freeway. One more block up from there is Kansas Street, a corner with one of the great views of downtown. From there, I walk north and east down the slope of Potrero Hill and across the South of Market flats to the Bay, sometimes walking over the low eminence of Rincon Hill. What I noticed most about the walk this week: It’s getting dark much earlier than it did just a month ago.