There's a handful of rivers/creeks around the northern reaches of Southern CA that seem like they would have narrow windows of opportunity for a packraft.
Piru Creek: from Pyramid Lake or just downstream if necessary to Lake Piru through Piru Gorge. (I've hiked up the lower reaches of the gorge on a relatively high water day and wished I had a packraft for the trip back down).
Sespe Creek: From Hwy 33 all the way out to Fillmore if you have the nerve/skill. There are some very technical sections in the lower reaches, especially during high water. Upper reaches seem pretty mellow as long as the water level isn't too high.
Santa Ynez River: Flatter water, mostly a float but a few sections that have small rapids. A handful of dams/reservoirs that you would have to portage. Goes for miles. I've "tubed" portions at moderate water levels.
Sisquoc River: Runs through designated wilderness, so long walk in to put in point(s). But then you've got miles of wild and scenic river with no obstructions (except for beaver dams!).
All four of these creeks have been run by whitewater kayakers on at least limited occasions (you can find some photos/documentation online). I don't know of anyone who has personally run any of these creeks on packrafts but it certainly seems feasible if you hit it during the (limited) prime water conditions.
Seems to be a somewhat fine line between too much water and too little with just a narrow window of opportunity between the two for these relatively small waterways. Anyway, I've considered a packraft just to add some new elements of adventure to trips through these areas.
