Mello-Roos is the common name for a special tax levied by a Community Facilities District under the Mello-Roos Community Facilities Act of 1982 (California Government Code section 53311 and following). Cities and school districts use it to fund infrastructure. It is not the 1 percent general property tax. It is an extra line, and it can run for decades.
The preliminary title report and the county tax bill show whether a parcel is in a district and what it billed last year. A sales flyer that ignores it is not a Loan Estimate. Lenders add the special tax to the housing payment.