which greatly resembles these schists. Good outlines of these mountains, indicative of structure, can be seen to great advantage from the San Luis Rey Mission. On the west slope of the San Onofre Mountains, 4 miles north of Los Flores, is an outcrop of a garnetiferous hornblende schist, which certainly appears to be in place. This rises 10 feet above the side of a gulch, and is fully 20 feet across. One mile north and in line of strike with the last is another outcrop of similar rock, which is so large that it certainly seems that it must be in place. The only point north of the San Onofre where this breccia appears is at Arch Beach, Orange County. The Santa Margarita Mountains are bordered by very extensive bowlder deposits, which rise as high as 1,500 feet on their western side. The topography of the northwestern part of the county between Temecula, Elsinore, and the ocean, is very complicated. This section is occupied by rugged, brush-covered mountains and narrow, deep valleys, with the exception of the Santa Rosa plateau, where the configuration of the county has been entirely changed by extensive lava eruptions, stretching over a distance of 10 miles. This mountain region narrows toward the north to form the Santa Ana range. The variety of rock formations is very large. The northern portion is unsurveyed. On the south are the two large grants, the Santa Margarita and the Santa Rosa. Between these lies De Luz Valley. The Santa Margarita Mountains extend north and south, forming the eastern borders of the grant and rising to an elevation of 3,100 feet. The granite of the region about De Luz Valley is far from being homogeneous. A part of it is undoubtedly intrusive, and a part may represent an original sedimentary formation. Bedding planes are present in much of this supposed metamorphic granite, but generally no schistose structure. The presence of the De Luz warm springs is perhaps due to a dike of dark, aphanitic diorite, which has cut through the granite in an irregular manner. A very interesting breccia outcrops in the bed of the creek below the warm springs. (Fig. 14.) [Illustration: Fig. 14.]