The present is the key to the past, but the past is generally believed to have been made up of relatively long and quiet epeirogenic periods separated by shorter times of orogenic disturbance. It is therefore important to decide whether the present is orogenic or non-orogenic.

In Central Europe, where the data are numerous, it can be shown that crustal movements of the present are perhaps ten times as great as those of the past, but the rate of movement is nevertheless small, and the comparison is less exact than could be wished.

The peri-Pacific region is in general better suited than Europe for a study of the problem, and California offers particular advantages. A compilation of the results of observations made by the writer and others in California shows that this region suffered a major orogenic disturbance in the Middle Pleistocene, at a time probably not more than 250,000 years ago. For this disturbance the writer proposes the name Pasadenan orogeny.

A study of this orogeny and of events following it suggests that, though its climax is long past, this disturbance has not yet completely died out. If this conclusion is warranted, the present does not truly reflect either the epeirogenic or the orogenic periods of the past, but is more disturbed than the one, and less disturbed than the climactic stages of the other.