Getting to Three Rivers

Three Rivers has no airports of its own, so you have three other options:

Visalia
Visalia is the closest city to Three Rivers, about 30 minutes away. However, it has a very small airport, and it is unknown if you can get a rental car easily at the airport. The only flights in are connections to other cities on the west coast.

Fresno
Fresno is a reasonably large city with a medium sized airport. You should be able to rent a car at any time of day, and there are many flights connecting to other cities, along with a few direct flights (but not many!). Fresno is about one hour from Three Rivers.

Bay Area or LA
After that, you're looking at flying into one of California's more metropolitan areas and driving down. This might be an option if you want to see some other relatives anyway. In this case, it's about a 4-5 hour drive from either of the metropolitan meccas to Three Rivers.