If you're stopping yourself from falling when running downhill, you're doing it wrong. You should be "leaning into" the hill, which is counterintuitive and feels like you're going to fall, but is way better for your knees and also faster than stopping yourself.
That only works for some grades. The grades in the Bay Area are pretty steep. If you leaned into the downward slope, you would be on your face in a few seconds.
