When a district is, for one year or more, in default in the payment of legally existing district obligations amounting to five dollars per acre or over, and an assessment has been authorized by vote of the qualified electors of the district as provided by section 48-3153, and levied by the district for the purpose of discharging the default or for the purpose of paying or refunding district indebtedness, or both, the assessment may be converted into negotiable first mortgage liens upon the lands located within the district and liable for such district taxes or assessments.
A.R.S. § 48-3160