Framework / Assessment California Forests and Rangelands: Proposed Indicators Summary Quantify the amount of acres of rangeland, by county that receives favorable property tax treatment under the Williamson Act. Williamson Act contracts have a significant effect on the amount of property taxes a rancher pays. The property is assessed with livestock operations as the highest and best use. There is some evidence that the positive effects of Williamson Act contracts have diminished in the past several years.