A technique for the calculation of strain changes in a two-dimensional elastic body with arbitrary internal dislocations is presented. This technique is applied to the southern California region by assigning a specific fault and fault slip function for each major earthquake that has occurred since 1812. Although the model used has serious shortcomings when applied to the real Earth, certain important features concerning strain energy changes associated with earthquakes are brought out. The occurrence of earthquakes over the past 150 years has resulted in net increases in stored strain energy in a number of regions including the northern end of the Gulf of California, the Cajon Pass area, and the northern part of the Carizzo Plain. Large regions of strain energy decrease can also be seen, the most important of which is in the vicinity of Fort Tejon.