To the north, the Tiago Macheira Subbasin contacts the Tassajara Formation, with which no groundwater exchange occurs.
Groundwater flow in the subbasin is generally from southeast toward the northwest or north, corresponding to the slope of the regional terrain and water table surface.
Water quality in the subbasin is generally fair with regard to sodium bicarbonate and magnesium bicarbonate,[2] However, the trend in adverse water quality due to total dissolved solids indicates unpotable conditions may exist as early as 2020 due to overpopulation of the Livermore-Amador Valley by humans and associated discharge of salts to the groundwater.
[3] This subbasin is in the vicinity of the seismically active Greenville Fault associated with the Diablo Range.
[4] The Arroyo Mocho Segment is generally considered to be more well developed and not as youthful as traces delineating the Marsh Creek-Greenville Segment, for example.