I grew up in a Hackamore tradition. It wasn’t the California one, it was the Texas one. However, since a horse is a horse, there is very little difference. We used snaffles too, and grazing bits, but colts were started in a hackamore. I got Ed Connell’s book The Hackamore Reinsman as a teenager, and I still go back to it for reference… and reverence!
For those who think they want to learn to use the Hackamore, i’d advise you to plan on taking lots of time, And finding a mentor. There are important rules to its use. My mentor summed them up back years ago by saying “Don’t hang on their head!” Others emphasize the rule “Only use one rein at a time, never both.” Another rule is “Never pull a steady pull on the reins, only pull and slack.” Pulling is really only done for the double, or the bending of the neck to turn a horse around when it gets too fast. As soon as possible using only the lightest vibration of a rein you “ask” for the horse to yield its “face” to you. This vibration or light bumping of the rein should become the signal. The technique bears many similarities to the modern concept of the “one rein stop.”
Lightness is the goal of Hackamore training, not contact. The only contact in a Hackamore horse is through the rider’s body, not his hands. The secret of a Hackamore horse is the use of the rider’s pelvis and seat bones to communicate with his mount. The rein cues are only an early pathway to developing a communication between the body of the horse and the body of the rider that is invisible. A concrete example of the psychology of hackamore training is the teaching of the neck rein signal. If you are turning right, you lightly rub the left rein on the neck of the horse while you turn your body to the right and emphasize your right seat bone. Then you bump the right rein, a slight pulling and releasing, like “set and release” several times, until he steps over to the right. After several repetitions of this, the next time you lay the rein on his left neck he will “hunt” the turn before you bump him. That’s when you quit for the day, to let him know “Yeah, you got it!”