(A) suite of models utilizing a simplified structural framework with a range of bulk rock permeabilities were developed to analyze the transient behavior of Basin and Range extensional geothermal systems, and particularly, the evolution of the system temperature with time. Each model consists of two mountain ranges (similar to1 km relief from the valley floor) separated by a thick sequence (about 4 km) of clastic sediments derived from the adjacent ranges, and a highly permeable, high-angle fault that functions as a conduit for subsurface fluids. This geometry is typical of Basin and Range extensional systems. We characterize the reservoir by utilizing several parameters, including temperature along the producing fault and the predicted surface heat flow. Time scales are on the order of 100 kyear for development of maximum reservoir temperatures. However, if not scaled, significant geothermal systems can exist on a steady-state basis. The models show some features seen in Dixie Valley, Naveda, and explain observed relationships that young faults are frequently associated with extensional geothermal systems. (C) 2004 CNR. Published by Elsevier Ltd. All rights reserved.