MAY 17, 1968 



MAY 16,1969 



Figure 10. Comparison of Bolinas Bay bottom contour maps of 17 May 1968 and 16 May 

 1969. Contours in feet. (Johnson, 1970.) 



Other data that provide information on the general movement of sediment in the entire 

 Bolinas Bay are presented by Wilde and Yancey (1970) who utilized heaw minerals as 

 tracers. Other supplementary data on sediment movement in Bolinas Bay resulted from sand 

 tracing studies along the beach face by the USGS during investigations of sedimentation and 

 hydrology in Bolinas Lagoon. (Gilroy, 1970a, App. No. 5.) This study used the placement 

 of fluorescent-dyed sand on the beach at both the town of Bolinas (Brighton Avenue) and 

 the Stinson Beach State Park with periodic detection of the direction of movement away 

 from the source by use of an ultraviolet lamp. Sand, at both localities, was placed on 23-24 

 July 1968, and then periodically sampled until late October 1968 when the dyed material 

 either was completely scattered and buried or the dye strength had been greatly reduced. 



The results of these limited and qualitative tests by the USGS showed that at Bolinas the 

 movement of sand was always eastward toward the entrance of Bolinas Lagoon, but no 

 material ever crossed the lagoon entrance to the Stinson spit. Although the surf observations 

 summarized by CERC showed a general westerly longshore current in this same locality 

 during the period of the sand tracing studies (Fig. 8), it is possible that tidal currents into 

 Bolinas Lagoon rather than wave-generated longshore currents moved sand generally 

 eastward along the beach. 



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