194 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 3 



of tidal water sweeps up the gradually narrowing channel of the Gulf and 

 causes an increasingly greater tidal range toward the Colorado river. At 

 Puerto Refugio the spring range is 11.8 feet, at Tepoca Bay 17.2 feet, 

 and at the mouth of the river 31.5 feet. These figures merely represent 

 the average differences between high and low water at the time of new or 

 full moon, and, since the author's visits to the Gulf were made during 

 times of maximum tidal difference in the winter and summer of 1940, 

 proportionally greater ranges were observed at all the stations visited. 

 Puerto Refugio, in particular, exhibited a most striking rise and fall of 

 the water level. A reef on the north side of the bay, exposed to a height of 

 at least 15 feet at lowest ebb, was completely submerged at high water. 

 At San Felipe on the Lower California coast quite near to the upper 

 extremity of the Gulf, large fishing boats were observed late in July of 

 1938 to be high and diy in a basin far above the reach of the high water 

 of that particular time. Yet, these boats are floated in on the crest of one 

 high-water tide and floated out again on another such crest. 



Two thirds of the way up the Gulf lie a group of large islands and an 

 outjutting peninsula of land which together serve as a very decided hin- 

 drance to the movement of water up and down the Gulf. Above this nar- 

 row "bottleneck" is a large water area connected to the southern water 

 mass and the ocean at large only through these straits. Consequent upon 

 the tremendous movement of tidal water in and out of the northern area, 

 very strong currents develop in the channels between the islands. On 

 either side of San Esteban Island the currents are so powerful that an- 

 chorage is impossible and must be sought in protected bays of the south- 

 facing shore. The significance of these currents in regard to the general 

 distribution of algal populations will be taken up in a consideration of the 

 oxygen relations of these plants. 



No discussion of general water movement in the Gulf is complete 

 without mention of the nature of wave action. Here again is a factor 

 playing an exceedingly important role in the oxygen relations of marine 

 algae. Unlike the outer coast, where powerful surf is the rule, the action 

 of waves in the Gulf of California is contrastingly slight. Except at times 

 of heavy winds and general storminess, the waters are essentially calm 

 and small waves prevail, breaking directly on the shore. Commonly there 

 is scarcely more than a strong lap of water on the beaches ; and, wherever 

 protection is afforded, little more than a gentle surge. Toward the south- 

 ern limits of the Gulf, however, increasingly heavy wave action is present, 

 reaching full proportions in the Cape district, where the collector, instead 



