The hike was pretty nice and definitely counted as an exercise. Santa Teresa park is a lot more open and barren than I expected, and the trails themselves are in full sun (even though scrubby shade trees are so close!). Coupled with an afternoon temperature at 90F it was sorta tougher than I expected. Oh, and, the trail gained altitude pretty quickly, much more quickly than I'd have thought. I think this means I need to look at more topo maps before choosing trails (the South Bay Trails book had only an area map and no topo data, and although it said "600' elevation change" I didn't have a good internal idea of what that would mean. Now I do). Anyway, I had brought plenty of water (Camelbak and a Nalgene bottle) so we survived just fine.
We finished the loop taking a shortcut (by repeating one stretch rather than taking an extra 0.1 miles to cover new ground) and were back to the car in about 90 minutes, a bit less than the 2 hours the guidebook expected. Along the way we saw: one runner; three mountain bikers (we were walking about the same speed they were cycling); one communications tower; one rabbit; several elderberry bushes; IBM Almaden Research Center; a great view of south San Jose (where suburbia meets rural land).