continental crustal evolution based on radiometric dating and distribution of rock units. His approach of weighing mineral dates against outcrop areas validated basic concepts of "orogenic periodicity" and established the basic pattern of global-scale episodic continental growth still recognized toady. Many of the questions and problems posed in Gordon's 1960 paper endure as central topics of research in the earth sciences today.

Russell Gordon Gastil was born in San Diego, California, June 25,1928 to Francis and Russell Gastil. By the time he reached high school, he was already attracted to geology as a profession because of the possibilities for exploration and discovery. He enrolled at San Diego State Teachers College (now San Diego State University) where he came under the influence of Professor Baylor Brooks, who later established the Department of Geological Sciences at SDSU. At the time, no geology degree was offered at SDSU, so Professor Brooks directed Gordon to the University of California at Berkeley, where he completed a B.Sc. in geology. He then continued on in the same department to complete a Ph.D., which he received in 1953. Gordon's doctoral thesis at Berkeley was a study of Proterozoic crystalline basement rocks in south-central Arizona, for which he had fellowship support from the Oak Ridge National Laboratory. He mapped and used a portable scintillometer to measure in situ radioactivity of rocks as part of this work; this experience helped establish his early interest in the rapidly developing techniques of radiometric datin.

Upon graduation and following a short stint working for Shell Oil Company, Gordon was drafted into the U.S. Army and served 22 months in southern Alaska and the Aleutians where he did geologic mapping with John Reed. Along the way, he collected granite samples for lead-alpha dating by Esper Larson at Harvard and subsequently did zircon separation work at the Naval Gun factory in Washington, D.C.

Following Army service, Gordon spent the next three summers doing mineral exploration and mapping in Labrador for a mining company (Canadian Javelin), spending the intervening winters in Montreal and at Harvard. He then returned to California, where he taught for three semesters at the University of California at Los Angeles before Baylor Brooks brought Gordon onto the San Diego State College faculty as a full-time faculty member in 1959.

Gordon received his first National Science Foundation grant at SDSU-for Pb-alpha dating-in 1961. In 1963, he and Ned Allison secured National Science Foundation funding to begin producing are connaissance geologic map of the State of Baja California. They hired six undergraduate students that first year (including two from Universidad Autónoma de Baja California in Ensenada), ordered air photographs, and the quest was on! Most of the mapping was done over the next four years but continued until it was compiled at a scale of1:250,000 in The map subsequently was published in 1975 as part of Geological Society of America Memoir 140, Reconnaissance Geology of the State of Baja California. What is remarkable about this mapping feat is not only that it was accomplished with undergraduate students, but that the general inaccessibility of large areas made the going extremely tough (at the time, there were no reliable topographic base maps and virtually no paved or graded roads). Along the way, Gordon mapped a large section of the State of Sonora, including Tiburon Island on the mainland edge of the Gulf of California. The Baja California map, published in three separate sheets and now out of print, remains as a primary regional mapping contribution still highly sought after by all Baja California geologists. It is certainly appropriate that these maps are being made available again in this volume as PDF files on the volume's accompanying CD-ROM.

Gordon's mapping experience in Baja California and surrounding areas formed the foundation of his research at SDSU. He has always freely shared his enthusiasm and ideas with students, colleagues, and anyone else interested in Earth. He ultimately supervised 58 master's theses at SDSU along with many dozens of undergraduate research projects known as senior reports. Most of this material has been published in some form, and a visit to the SDSU library to review thesis material is now almost a standard pilgrimage undertaken by anyone initiating new research or mining projects in Baja California.

Gordon's research on the tectonic and geologic history of Peninsular California and adjacent Mexico has established his position in the upper echelon of Cordilleran geologists. Highlights are almost too numerous to mention. He was the first to recognize the strong transverse asymmetry across the Peninsular Ranges batholith and its natural separation into distinct western and eastern provinces (a feature independently recognized by Lee Silver and co-workers at the California Institute of Technology). Building on work of Richard Mirriam and Esper Larsen, he also recognized contrasting patterns of pluton zonatin within the Peninsular Ranges batholith, including ring dikes and cone sheet structures in the western province. Following the arrival of Daniel Krummenacher at SDSU in 1969, Daniel and Gordon initiated two major projects in K-Ar dating. The first, across the northern third of the Peninsular Ranges batholith, documented the strongly asymmetrical west-to-east Cretaceous uplift and cooling history of the batholith; the second involved dating Cenozoic volcanic rocks in the circum-Gulf of California and relating this history to the evolving North American-Farallon-Pacific plate boundaries. Current knowledge of the pre-batholithic stratigraphy of Peninsular California is largely based on the work of Gordon and his students; much of this work is published in Geological Society of America Special Paper 279, edited by Gordon and Rick Miller.

Starting in 1973, with support from PEMEX, Gordon and his students initiated major mapping projects in the Vizcaíno Peninsula region of west-central Baja California that established much of the basic geology of the region, including documentation of ophiolite complexes. He did early work on the "elevated erosion surfaces" of the Peninsular Ranges, speculating on their tectonic significance. Together with students and using a magnetic susceptibility meter, he established the ilmenite-magnetite line within the Peninsular Ranges batholith and pioneered its use as a provenance tool in sedimentary successions.