Lassen County is on the Nevada border northwest of Reno.
Why are people leaving Lassen?
Lack of jobs, probably, and not high crime as implied in the headline. Anyway, the only reason Lassen County is mentioned is that it has a high percentage of people moving out, but the percentage is high because there weren't all that many people in the county to begin with. 7.5% of the 2020 population is fewer than 2,500 people. Many more people are moving out of the large cities.
Why are people leaving Lassen?
Move a dozen or so miles east and escape income tax and soooo much more!
Pro tip: don't do a 1031 exchange unless you really, really want to file 540 California state tax returns every year for 5 years and once more should you sell your new digs, or horrors! convert it to another use.
Even 20 or 50 years down the road you'll have to file one more 540 form so California can "CLAW BACK" their words, not mine, your tax savings!