Yesterday (8/11/13) my wife and I ran this section from the foot bridge near Heron Dam to the North boat ramp at El Vado on tubes.
There's definitely some huge boulders and narrow technical class III-ish rapids in that stretch, a little trickier than I anticipated. There was about 400-500 CFS I'd guess before the dam, although this isn't evident from the USGS gauges (La Puente gauge doesn't seem right...), an additional ~500CFS joined from the Heron Dam shortly after put-in (not sure where to get data for that gauge either so I'm guesstimating flows).
Between the bridge and the dam there is a long boulder field rapid I'd call a technical class III at that flow. I portaged the entrance though, and would likely portage it in any craft at that flow. The current converges on a single channel and piles onto a house-size boulder that splits the current left and right - right is fine, but left leads to a narrow gap between huge boulders, half the current was going in and flowing somewhere, it looked like a possible death trap sieve. I made a very short easy portage to avoid it, although at higher flows it appears the channel should open up more to the right, making it easier to avoid the left.
The rest was pretty straightforward, a couple more class III to III- and a couple of class II's. The first two miles are pool drop, the rapids weren't tough, but the boulders obstruct your view, making it tricky to scout. By the time you get into the lake bed, about halfway to the takeout on this short (~4 mile) run, the river opens into a wide open channel flowing pretty swiftly (constant small riffles, no major rapids) at least to where we took out for the boat ramp, the river went about another mile meandering through the lake bed past that point.
The North El Vado boat ramp is closed, so we had to hike to the gate. The hike was reasonable with tubes, and I think it would be good fun for IK's, but the hike would get ugly for rafts. From the riverbed, I'd say it's .4 miles to where we parked, it's a little muddy and eroded in the old lake bed, but easily passable. The .25 mile hike in is very steep, although well maintained, but if the river is lower you may have to walk to where the Lake Heron water comes in.
It's a very beautiful canyon and no paddle out now, just a bit of a hike for anyone who wants to see something different. Total solitude as well, it's an incredibly beautiful and unpopular run!
I took tons of photos, all the rapids from different angles, and then dropped the camera into the river right at the takeout
Hope this info is interesting to someone - oh, and if you want to run this stretch and can loan me an IK, let me know, otherwise I may toob it again in a couple weeks, but I'm not ready to hike my Puma in and out of there for a 4 mile trip. Next spring I'm definitely going to run it, the scenery is top-notch and the giant boulder fields are a lot of fun for me.