I know it’s hard, but IMO keep the yearling back east as long as possible. Even the best pasture around here hardly compares to a mediocre pasture back east and your youngster will have such an advantage galloping in large fields with groups of other youngsters learning and enjoying life as a horse.
I boarded my first foal at Saddlerock and even though she got to be in their biggest pasture in the most idyllic scenery, they just didn’t notice things in a timely manner such as illness or injury and made big changes in feeding practices without notifying me first. Maybe management is better now, but have heard similar stories of those who have boarded there… Swanhill in Moorpark is another that used to be okay, but nothing in comparison to what you might find back east. Daycreek might be your best bet locally. http://www.daycreekranch.com
Santa Ynez is your next best option, but have heard plenty of negative outcomes there as well. Definitely better options for your yearling up there though or maybe Ojai. I would also consider how each of these places will hold up to a Godzilla El Niño.
I know it is hard not to be able to see your youngster often and get to work with them, but having boarded a few babies locally and knowing many professionals around here who have done the same - much better to find a reputable place with real acreage and real pasture until your baby is closer to three. Better for joints, muscle development, coordination, manners, and mental health IMO.