Short-term and long-term slip rates are contrasted for 18 well-studied faults in the Basin and Range and Rio Grande rift provinces, over periods ranging from 3000 to 4,000,000 yr. The intrinsic variability of the 62 interval slip rates on these normal faults is assessed by normalizing the long-term slip rate of each fault to 0.1 mm/yr. The cumulative density function of the grouped data predicts that, given a mean net slip rate of 0.12 mm/yr, extreme slip rates with 10% and 5% probability of exceedance are 0.51 and 0.92 mm/yr, respectively. These slip rates are considerably higher than those chosen by an expert panel for the Pajarito Fault, New Mexico, which has a long-term mean slip rate of ca. 0.12 mm/yr.