Flat and boring, but I didn't know about the upper trail until reading another review. So, look for the upper trail and do not go in the heat of the day! There isn't much shade. I would do this walk in the evenings if I lived within walking distance, but it's not really worth a drive.
I walk this trail every morning with my dog and my husband walks it most afternoons with the dog. It is not difficult at all and provides a quiet walk with occasional sightings of wildlife (deer, coyotes, bears, etc.). In fact, we saw three does this morning on the "upper trail" (North Royal Oaks Drive). Family friendly and has two water stations near both ends of the trail for people and pets. There is a detour of an upper trail for about a mile that can be located on North Royal Oaks Drive.
Cheryl K. on Duarte Recreational Trail
This is one of those popular, friendly local walks in the San Gabriel Valley.
Nice wide dirt trail with a parallel asphalt trail. You can begin and end the trail behind the playground at Royal Oaks Park. This area is shaded, the rest of the trail is not.