54 
BUIylvETIN OE THE BUREAU OE EISHERIES. 
In attempting to present a plausible answer, reference is again made to the alluvial fan 
between the Santa Clara and San Benito Valleys. The growth of this great deposit, which 
swung the course of Coyote Creek from side to side, at one time into the Pajaro basin 
and at another into its former channel, was probably at the height of its activity near the 
time of the greatest coastal elevation, and then slowly ceased as the coast subsided. 
The lower course of the Coyote then, as at present, probably contained a fairly complete 
representation of the Sacramento fishes, it having direct connection with the river 
itself. The upper course would perhaps at no time harbor as many forms as the main 
channel, although any of its species might possibly be found there at periods of high 
water, and at the very time when a shifting of the channel would most likely occur. 
The first transfer of the Coyote was presumably made when the shore, of Monterey 
Bay was near the present 6oo-fathom contour, and the San Lorenzo was consequently 
a tributary of the Pajaro. This inflow of foreign water brought with it three species,® 
those which now inhabit the San Lorenzo and the Salinas, and all which at that particular 
time were contained in the captured portion of the Coyote. These forms eventually 
occupied the entire system, appearing in all its tributaries. The same cause which first 
turned the Coyote from its original channel would by its continued operation tend to 
shift it back again, leaving the Pajaro to itself as before. A subsidence occurring at this 
juncture drove the coast line back, submerging the lower part of the great valley, thus 
completely and permanently isolating the San Lorenzo with its three fluvial species. 
Again, the continued deposition of material on the plain where the Coyote emerged from 
the mountains turned its headwaters toward the Pajaro, bringing with it additional 
species, which easily reached the Salinas, but were barred from the San Lorenzo. 
Although the upper Coyote may have continued to swing back and forth over its grow- 
ing alluvial fan, no other species succeeded in passing until by the continued subsidence 
of the coast and the consequent retreat of the shore line the Salinas was finally detached 
from the Pajaro. Further shifting of the stream over the alluvial fan enabled other 
species to enter the Pajaro, but the Coyote at last returned to its original channel 
before representatives of all its native fishes had succeeded in crossing the watershed. 
It is especially significant that of the fishes which were presumably first trans- 
ferred to the Pajaro, and which have consequently been longest isolated from the parent 
basin, three have become sufficiently differentiated to be regarded as distinct species. 
o No account is taken of the possibility of the introduction of species which later became extinct, for the reason that the vol- 
ume of the San I^orenzo and all other conditions of the river and its surroimdings appear favorable to the support of at least 
some of the species not foimd there. It should be mentioned in this connection, however, that somewhat similar cases of unequal 
distribution do occur, in the streams tributary to San Francisco Bay, for example, for which no acceptable reason seems to pre- 
sent itself. The chance that species living in the basin have been overlooked is ignored also, because of the careful collecting 
that has been done in the region. 
It is barely possible that a close connection may at one time have existed between the Pajaro and Salinas Rivers, which 
was not mentioned in discussing those streams. On an examination of the map, plate xx, or on an inspection of the coast between 
the mouths of the Pajaro and Salinas, evidence appears which seems to indicate that the mouths of both streams, and especially 
that of the Salinas, are subject, or have been subject, to considerable shifting. This shifting is due directly to the piling up of 
drift sand, which in the case of the Salinas has apparently been crowding the mouth of the river northward until it is now in 
comparatively close proximity to that of the Pajaro. It is conceivable that this same movement may continue until a imion of 
the two streams takes place, and moreover one should not entirely overlook the possibility that such a union may have occurred 
before, and that the Salinas may even have received thereby a complete representation of the Pajaro fauna, certain species of 
which have since become extinct in that basin. 
