He, Ne, and helium isotopic measurements have been made on borehole fluids collected during drill stem tests at the Cajon Pass scientific drill hole. These fluids represent a dominant component (greater than 90%) of the formation fluids as determined from fluoroscein tracer measurements. The results indicate a crustally derived radiogenic helium source with excess He concentrations up to 100x air-saturated water conditions. The gas content and the chemical composition of the borehole waters reflect a variation in the formation waters entering the hole from several discrete, identified, and poorly interconnected fracture systems. These conditions indicate a local source for the excess 4He which allows 4He model ages of 33,000 to 5¿106 years to be placed on the formation fluids at this depth. This constraint suggests an upper limit of ≤7% of the total heat flow can be removed by hydrothermal processes. These data thus provide geochemical support for a low stress fault. These model ages further indicate an effective vertical component of the fluid transport velocity of the order of 0.04--6 cm-1. Pressure head and in situ permeability measurements indicate flow velocities of 10-5 cm yr-1. To satisfy both of these extant conditions, fluid exchange must have occurred (as least once) in the last ~33,000 to 5¿106 years under flow conditions considerably faster than presently operable. Fluid flow in this region is therefore discontinuous with long periods of slow flow interrupted by periods of very rapid transport. Such a conclusion is consistent with both local and general observations of metamorphic geology and suggests a deep crustal fluid transport mechanism that is mechanically and/or tectonically controlled. ¿ American Geophysical Union 1992