The migmatite exposures near Santa Ysabel, San Diego County, California, are pre-batholithi.c, and consist prima.rily of two rock types, tonalites and hornblende-biotite schists, with but minor biotite-bearing pegrnatites. The area mapped consists of three exposures and encompasses approximately an area 375 by 375 feet. From the apparent geological evidence, the basic schistose feet. From the apparent geological evidence, the basic schis-tose dikes intrude the tonalites with sharply defined contacts, and intude earlier basic schistose dikes with less defined contacts. Xenoliths of basic rocks, in various sta es of assimilation, and with some transaction by the basic dikes, occur in the tonalites; few ton lite xenoliths are evident in the basic dikes. The scbistosity of the dikes parallels the trend of the dikes and is controlled by flow ge during emplacement of the dikes rather than by metamorpbi.sm. Polymetamorphism is apparent from the several generations of transecting intrusive basic dikes, and from the textures of the rocks displayed in thin sections.