The report, by LA County Assessor Rick Auerbach, says the total assessed value of the county's commercial and residential property rose a strong 6.7% last year to a record $569 billion. The $36-billion gain is even better than the 6% increase posted a year earlier.

The higher assessed values means that the county's treasury is in for an unexpectedly large windfall because property-tax revenue accounts for a large piece of the local government's revenue pie. Moreover, Auerbach expects another 6%- to 7%-gain next year.

The report attributes much of the increase to the fact that many once-underutilized industrial properties are being spruced up or expanded—and thus their value enhanced—as the region's strong economy raises demand for warehouse, manufacturing and distribution space. The industrial vacancy rate in many parts of Los Angeles County has dropped below 4%, according to brokerage industry reports.