The trail is very popular with hikers, mountain bikers, and equestrians, so be prepared for company, especially on the weekends. The area is also rife with historical structural remnants, as it was a popular vacation/resort destination at the turn of the 20th century. A devastating flood in 1938 destroyed the roads and cabins, and pretty much wiped out Oakwilde, which I'll post about (our haunted hike) another time.
The trek to Gould Mesa Campground is fairly leisurely, and you'll pass by a couple shaded picnic areas (Teddy's Outpost and Nino) along the way.
As a sad postscript, the horrendous 2009 Station Fire damaged significant areas of the Angeles National Forest, and I believe that the Lower Arroyo Seco was not spared. Do check in with the local ranger district on trail conditions before heading out.
Camping: Gould Mesa is a hike-in trail camp with 5 spaces. The hike from the JPL trailhead is about 2 miles in. There are 3 hitching rails for horses and a vault toilet. No potable water except for stream water, which must be treated before using. First come, first serve only - no reservations. Call (818)899-1900 for more info.