My favorite California tree is Pacific Madrone. I love it even more than Manzanita! As far as I know, there is only one madrone tree at Rockville. And it is struggling! It's possible that its location is the problem, and it just doesn't have enough soil below it to thrive. But a more likely reason is twig die-back and/or trunk canker, both fungal diseases.
Update Oct 2018: another madrone tree! Very technically, it's on the other side of the park fencing, but I believe the tree is on park property, above Rockville Road. And it looks healthy!