1. Northward Extension of the Rancho San Marcos Dike Swarm: In Search of Silicic Dikes in Alta California Phil Farquharson SDSU - Geology 640 Spring 2000

2. Introduction n Rancho San Marcos Dike Swarm - a source for silicic volcanism? n If so, where are the resulting volcanic rocks? n What should we be looking for? n Swarm truncated on the north and south - may find continuation in bedrock windows

3. Topics of Discussion n SMDS Description u Location u Age u Structure u Chemistry u Petrography (to be done…) n Lake Jennings n South of the Agua Blanca fault in Baja California

4. San Marcos Dike Swarm Description n A densely intruded, northwest-striking, predominantly silicic regional dike swarm. n Exposed over an approximately 100 km-long segment in the west-central portion of the Cretaceous Peninsular Ranges batholith (PRB) in northern Baja California.

5. San Marcos Dike Swarm Location

7. San Marcos Dike Swarm Age

8. San Marcos Dike Swarm Structure

9. San Marcos Dike Swarm Chemistry

10. San Marcos Dike Swarm Petrography Work in progress...

11. San Marcos Dike Swarm Pictures Rancho San Marcos Area

12. San Marcos Dike Swarm Pictures Ojos Negros Area

13. San Marcos Dike Swarm Pictures Ojos Negros Area

14. San Marcos Dike Swarm Pictures Ojos Negros Area

15. San Marcos Dike Swarm Pictures Ojos Negros Area

16. San Marcos Dike Swarm Pictures El Alamo Area

17. Northernmost Extent in Baja California

18. Lake Jennings n Mapped by Gastil et al., 1961 n Sampled by Kimbrough

19. Lake Jennings Area Topo Map

20. Lake Jennings Area Geological Map

21. Other Possible Areas to Examine:

22. The BIG Picture: Shuttle Photo: STS064-080-021

23. Finis...