Field investigation indicates that the crystalline rocks of the Pajarito Mountain area, S.-central New Mexico, are intrusive rocks, probably Tertiary in age, rather than Precambrian basement bedrock as was previously thought. The geological evidence supporting this position consists of the discordant relation of the crystalline rocks to the adjacent sedimentary rocks, the zonation of the crystalline rocks from granite adjacent to the sedimentary rocks into a core of syenite, contact-metamorphic phenomena in the sedimentary rocks near the contact, and the presence of limestone and sandstone xenoliths in the marginal parts of the intrusive.

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