As EQ said, the property gets reassessed automatically when it sells. Thereafter, the maximum the assessment can increase is 2%/year. That’s probably why the one property has such a low assessment right now and the other one doesn’t.

In other words, if both properties were to sell for $400,000 each, they’d both wind up with identical or nearly identical assessments of about $4,500/year. The assessment is based on the most recent sale price.