Monday, October 24, 2005

Geog 316 journal - Point Reyes

Last weekend the class took a field trip to Point Reyes National Seashore see some examples of the concepts we discussed in class. Anyone who has looked at a map of the area and knows a little about geology may realize that the Point Reyes penninsula is very much an island. The San Andreas fault runs right through the Olema Valley and underneath Tomales bay - which I think is technically a large sag pond - creating the situation whereby the Pt. Reyes penninsula is on the Pacific plate moving slowly northward at a rate of a couple inches a year.

There were two concepts I really enjoyed learning on the trip, the first being the fact that the Bishop Pines are largely constricted to granitic soils and or bedrock. As I understand it the granites at Pt. Reyes were derived from the Sierran batholith by way of the Tehachapi mountains in Southern Ca. Nonetheless this fact really isolates the Bishop pine community and further emphasizes the island concept. It was good to see the amount of regeneration taking place and it sounded like the BP community was about due for a fire as they are fire adapted (the heat being neccessary to burst open the cones a germinate the seeds).

The other gem was Bolinas lagoon which is one of may favorite places anyway. Liam told us about his work there and I was intrigued by the sand lense that he has come across in many if not all of the corings from the lagoon. These layers of sand all occur on the same horizon and thus have the same date - sometime in the mid 1700's I think. Liam's major advisor Roger Byrne has posited that it may be from a tsunami that would have pushed over the sand spit at Seadrift. Apparently this event has been documented in other places. I'll be interested to the paper on this topic.

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