AbstractThe flow of ground water in a fractured rock aquifer may be linear toward a natural production surface rather than radial toward a pumping well, if the well penetrates a fracture having a permeability many orders of magnitude greater than the permeability of the surrounding aquifer. The well and its hydraulically connected production surface are called an extended well. Flow lines in a linear system are parallel, and drawdown is a function of the perpendicular distance from the extended well and not a function of the radius of the pumped well. The location of a concealed fracture and hydraulic diffusivity of the linear system can be determined if drawdown data from two observation wells are available.Linear flow has been recognized in fractured rock aquifers from aquifer test data in three widely separated areas of New Mexico and probably is the cause of the anomalous response observed in fractured rock aquifers in Mendocino and Placer Counties, California. Test data were curvilinear on semi‐log plots and straight lines on log‐log plots, suggesting that traditional methods of aquifer test analysis are not applicable. Straight lines could be fitted to arithmetic plots of pumped well and observation well data when plotted as drawdown versus √t, indicating that the flow in the vicinity of the test well is linear. Linear flow may be a common phenomenon that has been overlooked in the analysis of aquifer tests in fractured rock aqu