736 WN. H. DARTON 
not revealed, although probably not far below the bottom of the 
valleys. 
In the Arroyo San Gregorio, about 6 miles southwest of La 
Purisima, the yellow beds are exposed lying on Monterey beds and 
overlain by mesa sandstone. ‘They thin rapidly to the north where 
the surface of the Monterey beds rises rapidly. ‘The yellow beds 
outcrop prominently again near Purisima Vieja, 1o miles north- 
west of La Purisima, exhibiting all the strata down to the richly 
fossiliferous limestone bed which occurs at the base of the forma- 
‘tion near La Purisima. The following section is exposed in this 
vicinity. Probably Monterey beds are not far below the bottom 
of the arroyo at this place. 
The stratigraphic relations of the yellow beds are extensively 
exposed in the Arroyo de la Purisima from near its mouth to a point 
Fic. 15.—Section in the Arroyo San Raimondi northwest of La Purisima, Baja 
California. a, agglomerate; m, Monterey beds; g, Quaternary. 
about 6 miles above La Purisima where the base of the overlying 
mesa sandstone crosses the canyon. ‘The principal features are 
shown in the cross-section 14, Figure 2, and the columnar sections 
in Figure 17. For some distance near the 1,360-foot boring the 
yellow beds may either thin out or give place horizontally to a 
massive bed of conglomerate which lies on the Monterey beds; the 
precise relations are obscured by talus which breaks the continuity 
of the outcrops. The view, Figure 18, shows high cliffs ro miles 
below La Purisima where the yellow beds include a massive member 
of impure limestone filled with fossils, apparently the same bed as 
the first: one rising above tidewater several miles southwest (see 
Fig. 17, sec.1). This bed appears either to thin out or to give 
place to sandstone and agglomerate farther north near the drill 
hole. There are extensive exposures of yellow beds about La 
Purisima (see Fig. 19) with a basal member of limestone filled with 
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