This is the most easterly of four sodic intrusive complexes (Nos 2-5) aligned east-west and extending over 70 km (Daugherty, 1966). They lie only a short distance south of La Cueva (No. 1) and east of the Terlingua-Big Bend area of Texas (U.S. No. 105). Each intrusion apparently has a core surrounded by one or more rings, and three of the intrusions display magmatic doming, cauldron subsidence and ring dyke formation. Aegirine, nepheline and analcime-bearing syenites are prominent in four of the intrusions. Levinson (1962, p. 68) describes the central plug at Aguachile as consisting of a quartz microsyenite containing riebeckite and McAnulty et al. (1963) refer to the presence of dykes and irregular intrusions of teschenite.