6 The Delta of the Rio Colorado. 
miles farther south within the memory of certain Indians, and also by 
the formation of Hilda Island in the lower reach of the river, which 
is recorded on the accompanying map for the first time, and which 
was first noted by Mr. Godfrey Sykes while descending the river in 
the sloop Hilda in 1890. 
The sparse records of the last century show that islands have 
appeared and disappeared in the lower reaches of the river in a very 
2 
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RAD 
a Honea Isreet 
oh ase 
3S 
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6° 
FIG, 3-—-SKETCH OF THE MOUTH OF THE COLORADO RIVER MADE BY LIEUTENANT DERBY 
IN 1850, sgh pit SLIGHTLY FROM THE GENERAL MAP OF THE WHOLE 
MADE BY HIM AND MAJOR HEINTZELMAN, 
capricious fashion. The funnel-shaped head of the Gulf of California 
shoals abruptly in the mouth of the river, and flood-tides reach a 
height of forty-one feet above low water. These conditions lead to 
the formation of a bore which sweeps upstream at the close of the ebb 
in a comber four to six feet in height, striking the exposed shores 
with great violence and starting new points of erosion and shoal 
deposit. Within the region affected by the tides, the tules and tall 
ees See aoa cca erg eres ee Kiarome SRE pe eer ie 2 
aa IS Pi op Ce ce aa SS) ee ees 
