Root zone soil moisture is a dynamic variable subject to rapid changes in time as well as space. Ground based methods for measurement of temporal and spatial changes in root zone soil moisture require much time and effort and, therefore, have limited value for soil moisture monitoring at the watershed and river basin scale. Remote sensing methods using radar imagery measure soil moisture near the soil surface. We analyze optical imagery (Landsat, MODIS) with the New Mexico implementation of the Surface Energy Balance Algorithm for Land (SEBAL^NM) to determine the regional distribution of the evaporative fraction. Next, we derive root zone soil moisture from a semi-empirical relationship between evaporative fraction and root zone soil moisture.