Jackson County, Oregon
That's just over 300 miles by car. I've been to every county in CA and NV.
Hit this in November of 2019. I think Lake, Oregon is probably the next one.
Over two years later and it’s still Lake, Oregon for me.
Looking at a map, once I get Lake and Harney in Oregon, it’ll be a toss up between a lot of counties. Oregon, Idaho, Utah, and Arizona all have possible contenders.
Edit:
Closest counties:
1. Lake, OR
2. Harney, OR
Approximately a three way tie by road distance, ordered by straight line distance:
3. Grant, OR
4. Juab, UT
5. Payette, ID