Several chapters in this volume describe various aspects of the tectonic evolution of the Gulf of California, including detailed models of the current regime of active extension in the southern gulf and the northward transition to the strike-slip San Andreas system. Tectonic models can be tested for consistency. Geodesy makes direct measurements of relative motions between lithospheric plates and thus allows tests of the models. Unfortunately, for many geologic applications, extremely high geodetic accuracies may be required to obtain results even on decade time scales, and potential measurement sites (on separate plates or fault blocks) may be separated by large distances (> 100 km), too great to be spanned by conventional terrestrial geodetic techniques operating in a line-of-sight mode. Fortunately, space-based geodetic techniques are becoming available that promise high horizontal position accuracy (better than 1.0 cm) over distances of 1000 km or more. Such techniques are particularly desirable for measurement of total relative plate motion whenever the plate boundary is a broad zone of deformation, e.g., southern California and northern Baja California, or if large distances separate potential measurement sites, e.g., the southern Gulf of California.
Thus, the two chapters in this section review the status of space geodetic measurements in the Gulf of California. CHRISTODOULIDIS et al. describe Satellite Laser Ranging (SLR) results obtained by NASA’s Crustal Dynamics Project. These data have already permitted an estimate of the rate of motion between Mazatlan on the North American plate and several sites in California on the Pacific plate, and they