The under­ly­ing rock of the Puente Hills from the Bed­ford and South­ern Cal­i­for­nia Batholith base­ment to the Miocene and Pliocene sand­stone, silt­stones, and shale tells us a story about the nat­ural his­tory of the Puente Hills, about how they were made and how they came to be Hills. This was not a short process. Time passed slowly but […]

The third event recorded in the rock of the Puente Hills is the lay­ing down of thick rock lay­ers, which were sub­se­quently uplifted. For over 10 mil­lion years in the marine basin opened by the rota­tion of the Trans­verse Ranges, the Los Ange­les Basin and the nascent Puente Hills accu­mu­lated thick lay­ers of sed­i­men­tary rock. The […]

The sec­ond event recorded in the rocks of the Puente Hills began some 23 mil­lion years ago. The trench sys­tem, which had for so long dom­i­nated the for­ma­tion of South­ern Cal­i­for­nia, ended around 28 Ma, when the Pacific Plate trans­form con­ver­gence replaced the Far­al­lon Plate trench sys­tem. As the “trail­ing edge of the Far­al­lon Plate entered the […]