Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

Keith K. Klepeis

Second Advisor

John Lens


The Laramide orogeny is one of the most important tectonic events in western North America’s geologic history. The Southern California Batholith (SCB) contains geologic information about the deformational history of the initiation of the Laramide orogeny during the Late Cretaceous (100-70 Ma). The beginning of the Laramide orogeny is defined by a transition from thin-skinned to thick-skinned tectonic deformation. There have been many geologic models attempting to describe why and how this transition happened, but no models have been fully accepted. I compare two recently proposed models that have fundamental differences in the style of deformation and sense of shear of the initiation of the Laramide orogeny. I used field observations and structural measurements to perform structural and kinematic analyses to determine a relative structural deformational history of the SCB in the San Gabriel block of Southern California. By analyzing these data, I am able to determine the style and sequence of deformation and establish a general history of fault block rotation. Through structural and kinematic analyses, five Cretaceous-aged ductile deformation events (D1-D5) were identified followed by three major brittle faulting events that uplifted the San Gabriel Block. D1/D2 are characterized by granulite facies metamorphism, ductile top to the south thrusting that is related to the Early Cretaceous Sevier orogeny. D3 is an amphibolite facies metamorphism event that initiated the development of the Cretaceous Black Belt and Cucamonga shear zones. This event records a top to the SW transport for the Laramide orogeny during sinistral transpression. D4 formed southwest verging macroscopic folds that formed during syn-tectonic intrusions. D5 produced a sub greenschist fold-thrust belt from late brittle faulting. The subsequent brittle faulting events can be correlated to the surrounding Cucamonga, San Antonio Canyon, San Jacinto, and San Andreas faults. By comparing the results to the two endmember models of the Laramide orogeny I conclude that the “Magmatic Flare Up” model best describes the deformational history identified for the SCB. The “Hit and Run” model is a good fit for most of the northern part of western North America Cordillera, but not south of the Sierra Nevada batholith. I conclude that the Insular superterrane collided into North America during the Late Cretaceous north of the SCB and that the conjugate Hess oceanic plateau subducted beneath the SCB initiating thick skinned deformation and shutting off magmatism around 75 Ma.



Number of Pages

125 p.

Available for download on Thursday, June 12, 2025