A PropaBLe Orietn or THE Numerous DEPRESSIONS IN THE 
Mesa Sour or THE Arroyo ForMED BY THE OUTLET 
or T1gERAS CANYON 1N THE Sanpras NEAR 
ALBUQUERQUE, NEw Mexico. 
By ALBert B. REAGAN. 
The occurrence of humerous slight depressions, thickly distributed 
over the mesa south of Tijeras arroyo on the east side of the Rio Grande, 
south of Albuquerque, New Mexico, is very noticeable. These were ob- 
served to be rarely more than five yards across and commonly from eighteen 
inches to two feet in depth and are provided with a raised border. They 
resemble buffalo wallows very much; but are too abundant and their dis- 
tribution is too general. The stratum in which they are indented is a very 
loose, unlithified formation, superimposed upon the Albuquerque Marl,* a 
calcareous deposit some six feet in thickness. 
The depressions extend in depth to this marl stratum and seem to hold 
water. 
These depressions seem to be the “blowouts” of mud upheavels. They 
seem to have been formed at the time the Albuquerque marl was in a semi- 
fluid state. The loose unlithified stratum that is superimposed upon the 
marl was washed down from the Sandias onto the area faster than the 
marl could harden or “ereep” from its advance over the bottom of the 
then Albuquerque lake which occupied the Rio Grande embayment at that 
point. As a result of the pressure caused by the superincumbent weight, 
mud lumps formed in size proportionate to the pressure, like those now 
forming in the Mississippi Delta.** And like those of the Southeast Pass 
of that delta, they collapsed on reaching the mature stage, leaving a small 
pit surrounded by a raised ring. Thus the mud lump, “blowout” theory 
seems to explain the origin of the depressions. 
*C. L. Herrick. The Geology of the Environs of Albuquerque, New Mexico. Amer- 
ican Geologist, Vol. XXII, pp. 29-33. 
**E, W. Hilgard. The Exceptional Nature and Genesis of the Mississippi Delta. 
Science, Vol. xxiv, pp. 861-966. 
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