114 
FOURTEENTH REPORT. 
NOTES ON THE GEOLOGY OF THE GAL LINA, NEW MEXICO, 
QUADRANGLE. 
BY E. C. CASE. 
During- 1 lie summer of 1911 the author had an opportunity to examine, 
somewhat hastily, the geology of the region around the Mesa Prieta in 
the Gallina quadrangle. The points which it is desired to bring out in 
these brief notes is the close relation which exisls between the structure 
of the region and the drainage of the country. The central portion of 
the quadrangle is occupied by the great Mesa Prieta, a block composed 
largely of Triassic and lower “red beds,” capped by Jurassic and Cre- 
taceous. The aridity of the area resulting in the sharp erosion features 
of such a climatic region brings into sharp relief the structural features. 
The Mesa Prieta is separated from the Mesa de los Yiejos on the 
northeast by a sharp fault occupied by the valley of the Chama river. On 
the southwest side of the mesa a second sharp fault separates it from the 
San Pedro mountains, this line is occupied by the intermittent streams 
called Poleo and Capulin Creeks. A glance at the topographic sheet 
shows that these two valleys are almost parallel in a northwest south- 
east direction. The structure of the San Pedro Mountains is totally dif- 
ferent from that of the Mesa Prieta but the Mesa de los Yiejos is nearly 
the same. The north side of the Mesa Prieta was not examined but a 
consideration of the map shows a series of small stream courses running 
into the Chama from the southwest and in many cases the mouths of 
these streams are almost exactly opposite the mouths of streams which 
enter the Chama from the northeast, running off of the surface of the 
Mesa de los Yiejos. It was evident from a survey of this mesa made 
by a powerful glass from the surface of the Piedra Lumbre that these 
small valleys were on lines of breakage in the large mesa. The canon 
of the Arroyo Secco and that of El Cobre Canon, not shown on the map, 
but paralleling the Arroyo Secco on the east, are larger valleys along 
fault lines. 
In the same line as the valleys just mentioned is a series of valleys in 
and on the borders of the Mesa Prieta to the east and southwest. The 
valley of Ihe Pnereo river runs in a nearly northeast southwest direction 
and a second great fault forming ihe cliff of the Mesa Prieta on the 
south easi side runs in the same direction and is apparently a direct 
continuation of the line occupied by the Arroyo Secco. Between the 
Mesa Prieta and the Capulin Mesa, a western portion of the same block, 
there is a sharp valley occupied by an intermittent tributary of Capulin 
creek. Between the Capulin Mesa and the Cerro Blanco is another 
sharp break parallel to the other lines mentioned. The valley of the 
Gallina river does not occupy a fault line but is guided by the upturned 
edges of the Mesozoic strata which here dip sharply to the west or 
northwest and within a short distance are overlain by the horizontal 
strata of the Pnereo and Wasatch Tertiary beds. 
