Just moved here from the OC. Looking for a trail that is similar to Whiting...uphill and downhill and fast bottom section. Rode JPL once....a little scary on a stretched out XC.
I like climbing Chaney Trail to Sunset. It's a short loop - faster and more technical than JPL / El Prieto. There is also much less stream crossings. If you have time / legs, you can climb all the way up to Inspiration Point and descend Middle Merrill and traverse back across to Sunset. If you are looking for fun, but less technical rides - look at Marshall Canyon and Turnbull Canyon - but both are more of a drive from Pasadena.
Chantry flats has upper/lower Winter Creek, and many other options. More exposure than any part of Whiting, but damn awesome trails. Very doable on an old rigid steel hard tail.
I think you would enjoy Cherry Canyon. There are some similarities to Whiting Ranch: Lots of ups and downs rather than all up-all down. Only mildly technical. Fast, rhythmic bottom section (not as long as Sage-Cow-Live Oak), but still fun. I like to start from Hahamongna Park near JPL and ride the Flint Canyon trail on the way out and the way back. You can also use Ridge Mtwy to connect over to the Catalina Verdugo trail, which is a nice singletrack loop around the Glendale Sports Complex. Here's an example of a short version: https://www.strava.com/activities/439414786 And here's an example of a longer version: https://www.strava.com/activities/432808652 It's not the easiest place to navigate, so first time out it would be best to ride it with someone who knows the way. Shoot me a message here if you would like to join in for a ride sometime. My wife and I ride out there often.