It can take some looking to find Pteronarcys. They are easiest to locate by looking for large substrate pieces...
So, if you want to find more, be sure to check the larger subsrate pieces in your stream -big boulders, and wood, that collects leaf pack. This is more work and lots of samplers don't bother. You'll also find other large stoneflies, Corydalids, and craneflies, and crayfish too.
Good advice Paul. I have actually found them in old terrestrial beetle galleries in submerged logs.
My experience with californica is they ball up in the hand, not in the water. I've experimented with them quite a bit. My theory is that they behave somewhat like pill bugs? It's a predator response not a lost footing one. I found that if you hold them before dropping in the water they will often stay curled for quite awhile until they are sure they are safe from the critter that grabbed them. When gently shaken off rocks held low in the water they usually drift arched the other way with their legs held out looking to get ahold of something. They will tumble somewhat but mostly they will right themselves at some point. If I then reached into the water to grab them or touch them, they often curled up again. Anyway, That's why I tie my imitations on straight hooks or slightly bent up, at least for californica.
Perhaps their lack of numbers is why they are prone to seek out more protective homes?