G. K. Gilbert— Outlet of Lake Bonneville. 347 
Passing now from the subject of the general position of the 
outlet to the question of its precise location at the time of the 
commencement of the outflow, I find myself able to make a 
concession to Dr. Peale. I at first supposed that the divide 
originally lay between Red Rock and Hunt's Butte, just as it lies 
to-day, and I so described it. A careful reéxamination of the 
locality has convinced me that I was in error, and has led me 
to assign it a position two miles north of Red Rock. Dr. Peale 
placed it about forty-five miles north of Red Rock, so that my 
new determination is nearer to his than my old was. 
With the aid of the accompanying map I hope to make the 
chief topographic features of the locality, and the history of 
the outflow, clear to the reader. 
At the point of greatest orographic constriction, that is, where 
the mountains bordering the general trough, approach nearest 
to each other, there is evidence of a connecting ridge of lime- 
stone. This ridge is so low that only a few peaks of its serrated 
crest project through the superficial deposits. To it belong 
Red Rock (R), Hunt’s Butte (H) and the hills marked L, L, L. 
Just north of the ridge Marsh Creek issues from the moun- 
tains at the east. It flows southwestward for three miles, 
makes a sharp turn about Hunt's Butte, and then flows 
Dorthward to Marsh Valley, occupying the old river bed 
all the way from Hunt's Butte. It is the largest stream of 
the vicinity of the pass, and has thrown so much debris into 
the river bed that it has determined the modern divide at the 
point of its accession. It is contained by high banks all the 
way from its mountain cafion to Hunt’s Butte and has no free- 
dom to shift its course over its own alluvion until it enters the 
higher than the original divide. As the channel of outflow 
deepened by wear, the lake level was lowered and its shore 
retreated southward. The head of the outflowing stream fol- 
