The examination of samples collected at two locations, one in the northern part of the Santa Fe quadrangle and the other about 4 mi. N., in the Tesuque quadrangle, discloses the presence of amorphous gypsum in amounts ranging from 55% to 88% in the silts and sands of the upper beds of the Bishop's Lodge member of the Tesuque formation [Tertiary]. Intense chemical weathering was noted in the volcanic and granitic components of the playa beds, and the theory is offered that frequent wetting and dessication during deposition were responsible for mildly acidic solutions which could have caused the chemical weathering observed. The discovery of a marked disconformity at the top of the playa beds separating them from the overlying Tesuque formation, coupled with changes in lithology, mode of sedimentation, and nature of terrain supplying the sediments, suggests that the Bishop's Lodge member and beds underlying it should be separated from the Tesuque formation.

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