474 J. J. Stevenson— Geology of Galisteo Creek. 
whereby this fragment of Dakota has been thrust through the 
Laramie rocks. The two faults come together on the north side 
of lower Galisteo at the mouth of the Arroyo and the Dakota 
rocks do not cross the creek. The Colorado shales do not ap- 
pear on either side of the faulted area. 
ut on the west side of this arroyo there appears a series, 
newer than any yet noticed. It covers the mesa stretching 
west and north from the Galisteo, and is continuous from the 
Santa Fe and Placer road on the lower Galisteo almost to the 
end of the Archean area on the upper Galisteo. This is the > 
Galisteo group. As far as exposed within the area examined, | 
which extends to but a little distance west and north from Ga- 
listeo creek, this group is 
1. Breccia of trachyte-____-- 150 feet. 
2. Soft, light gray sandstone__ 40 feet. 
The breccia is well shown on the lower Galisteo from the Santa 
Fe and Old Placer road to the mouth of the Arroyo de los An- 
geles. It is exceedingly dark gray or even lead-colored and is 
composed altogether, where examined, of trachyte in angular 
fragments, cemented by ‘finer material apparently of similar 
nature. This breccia was followed up the Arroyo to the Galisteo 
and Santa Fe road ; but there it practically ends, and the evi- 
the underlying sandstone are ex posed here and are conformable. 
__ The Galisteo beds are not affected by the faults found in the 
from Los 
the north 
