that have been driven into the ground to the ground surface. The pipes 

 were then set in place with concrete to a depth of 24 inches. The sea- 

 ward pipe was capped with a 3-inch brass plug that has the bench mark 

 designation engraved on its upper surface. The bench marks were desig- 

 nated SIO I (South Range), SIO II (Indian Canyon Range), and SIO III 

 (North Range) as shown below: 



© 



The primary bench mark, as described above, was placed in the bed- 

 rock at the landward margin of the beach. This location allowed both 

 ready access for survey use and also provided some protection from loss 

 by erosion of the beach. A secondary bench mark was placed on the range 

 about 50 to 100 feet landward of the primary bench mark. These bench marks 

 were necessarily located up on the talus slope at the base of the sea 

 cliff and are identical to the primary bench mark except that the pipe was 

 not capped. Elevations of the bench marks for each range are given below: 







Elevation of 



Elevation of 





Bench 



Primary B.M. 



Secondary B.M. 



Range 



Mark 



Rel. MSL 



Rel. MSL 



South 



SIO I 



8.77 ft 



42.67 ft 



Indian Canyon 



SIO II 



9.98 ft 



29.92 ft 



North 



SIO III 



10.91 ft 



32.10 ft 



Alinement on the range line is accomplished by using flags to mark the 

 two bench mark pipes so that the rodman or boat operator can position a 

 point on the range. Distances along the range are determined by tape 

 measurement from the primary bench mark or by plotting the boat position 

 from horizontal sextant angles between flags marking adjacent ranges. 

 Elevations along ranges are determined by surveying a level line from 

 the primary bench mark. Fathometer soundings are corrected to mean sea 

 level to provide the corresponding data offshore. The onshore and off- 

 shore surveys are combined into a single profile by referencing all 

 data points to the MSL datum. 



43 



