Did the loop and added in the Mount Lowe Loop too.
I've run and hiked this loop dozens of times. This a great complex of trails to have so close to the city.
Hiked up Lower Sam Merrill trail to Echo Mountain. Continued on the loop of Castle Canyon and Middle Sam Merrill trail back to Echo Mountain. Lower Sam Merril trail back to Cobb Estate. Beautiful nice and sunny day in early March. Great views.