Land subsidence is one of the six sustainability indicators that must be managed without causing undesirable results in a Groundwater Sustainability Plan. Technical Consultant Lynn Groundwater from Provost & Pritchard reviewed maps at the Ad Hoc Technical Committee meeting showing historic and current information on subsidence in the McMullin Area GSA territory.

Land subsidence occurs generally where the Corcoran Clay underlies the Valley, but recently land subsidence has been documented in some areas not underlain by the Corcoran clay.  The map below (click on map to enlarge) shows land subsidence from 1926 to 1970. This historical map shows subsidence as one foot in the middle of the McMullin territory and 4 feet in the upper left of McMullin’s boundary.

A more recent map from NASA shows the amount of land subsidence from May 2015 to May 2016 (click on map to enlarge). The green areas represent less subsidence. The yellow to orange areas are higher. The coloring within the McMullin Area indicates that subsidence varies across the territory. On the eastside of McMullin there has been minimal subsidence with it increasing as you go west. Overall there was less than 5 inches of subsidence from May 2015 to May 2016 in the McMullin Area GSA.

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