Check OnX property boundaries, USFS Motor Vehicle Use Maps (restrictions, closures, dates, etc), and even google earth for access to those little roads. A lot of those little marked roads start on gated private property. I cannot vouch for 35/Mosher with ground verification, but it appeared landlocked/gated on maps.
Do you get altitude sickness? We camped at 10,000+ last year coming from ~2-3K and we had to bail down before season started, buddy got real bad altitude sickness. If you do or are unsure, may be helpful to sleep below 8k' or to take a few days before season starts to acclimate before sleeping at higher elevations. I'd take the former route if you are time limited. We slept at around 7,500 and he was better by the next day and was able to hoof it during the day at 8,000-10,500 for the next week. If you do cardio I bet you will be just fine, coming from that low I'd focus on heart/lung/mental workouts over legs or core work.