23iB Dicker son: Baguio Plateau 433 



In connection with this major faulting, incidental movements 

 along the east and west cross faults which cut the Santo Tomas 

 Trail probably occurred as well. Now pour into these newly 

 formed trenches torrential tropical rains and with exceeding 

 quickness a deep canon is developed. If this reasoning be cor- 

 rect, then this faulting must have taken place during the late 

 Pleistocene and may have been incidental to the general uplift 

 of Baguio Plateau. Since earthquakes are frequently reported 

 at Baguio, it is highly probable that seismic disturbances still 

 continue along these faults at the head of Bued Eiver. The 

 fact that the hanging valley of Loacan still remains further 

 indicates a late Pleistocene age for these events, since hanging 

 valleys, like lakes, are but transient physiographic features 

 Faulting may also have aided Gold Creek and Antamok River 

 in beheading the Loacan, as a very prominent northerly trend- 

 ing fault occurs in Antamok Valley near the Benguet mine 

 This fault has brought the older diorites in contact with the 

 late Miocene andesites. 



TRINIDAD VALLEY 



The most-striking feature seen on the topographic map of 

 Baguio Plateau is the wide, round, sparsely contoured spot indi- 

 cating Trinidad Valley. Not only is this true upon the map, 

 but the intelligent nontechnical visitor to this valley sees the 

 striking contrast between the narrow gorge of Trinidad Creek 

 and the even valley floor beyond. At once he seeks an explana- 

 tion, and the current hypothesis of volcanic crater develops as 

 soon as the craterlike form is observed. It is not the writer's 

 intention to waste too much time bowling over a "paper man," 

 but a little explanation is due the layman. If a volcano were 

 suddenly formed in an area of nearly horizontal sedimentary 

 rocks then, with the upthrust, the sedimentary rocks would be in- 

 clined away from the center of the volcano on all sides, and the 

 lavas or mud flows would be poured out across the broken edges 

 of the sedimentary beds and form lava or mud-flow slopes com- 

 pletely burying the sedimentary beds for a time. Later dis- 

 section after the volcano became dormant would partially ex- 

 hume the sedimentary beds and a concentric arrangement would 

 be found due to the more easily eroded sedimentary beds. Such 

 a case occurs in the center of the Sacramento Valley, California. 

 The Marysville Buttes, "the stump of an old volcano," consist of 

 a central core of a coarse-grained lava, andesite, which was 

 forced up in the valley floor, a ring of marine sedimentary rocks 



