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SEVIONFOUR Seismic Hazard Inputs which is a partial update of the Wells and Coppersmith (1994) relation that they developed to remove a proposed bias in the dataset due to oversampling of smaller-sized events. The Stirling et al. (2002) censored relation better fits the paleoseismic data of normal where abundant displacement data are available and was included by the Working Group on Utah Earthquake Probabilities in their forecast for the Wasatch Fron region(Lund,2012; DuRoss et al.,2015). To account for the various uncertainties in estimating maximum magnitudes (e.g., dePolo and Slemmons, 1990), we also included ± 0.3 magnitudes (weighted 0.2 each) for all of our maximum magnitude distributions (Table 1). Length estimates are taken from mapped fault lengths and are measured end-to-end in a straight line. Depending on the available data, we used both slip rates and/or recurrence intervals to characterize rates of activity (Table 1), generally preferring the latter based on arguments in Wong and Olig (1998). However, the only fault with recurrence interval data is the Sawatch fault so we heavily relied on slip rates. We incorporated all available long-(<_ 1.6 Ma)and short- term (<_ 130 ka) data in developing slip rate or recurrence distributions, but we generally preferred short-term data whenever it was available. In addition to the time period, we also considered the type and quality of data in determining slip or recurrence rates. Whenever possible we attempted to calculate or adjust for along-strike average net slip rates. For example, we converted vertical slip rates to net slip rates for most faults by assuming 100% dip-slip and the preferred fault dips. Therefore, for a typical range-bounding normal fault with a preferred dip of 50°,this results in a 30% increase when converting vertical slip rates to dip slip rates. For a steeper dip of 60'the increase is less at only 15%. Variations in displacement along strike can significantly affect the calculation of slip rates (Wong and Olig, 1998), but unfortunately there are very few faults for which we have enough data to calculate average rates for the entire fault. More typically there are only a few data points at one or two sites along the fault or no fault- specific data at all. In the latter case, we assumed slip rate distributions to be the same as a similar, nearby structure, taking into account factors such as style of deformation, geomorphic expression,and age of youngest movement. Due to its length, rate and proximity,the WFMF is the most significant contributor to the hazard at the Henderson site. Therefore,this fault and its seismic source characterization are discussed further below. Due to their proximity and apparent relation to the WFMF, we also discussed the source model for the unnamed faults in Williams Fork valley. For more details on the mapping, paleoseismology and related geology of these faults see Kirkham (2004), Kellogg et al. (2011), and Olig et al.(2013). Williams Fork Mountains Fault The WFMF (USGS# 2301) is located in the northern Rio Grande rift, north of the Frontal fault and south of the Steamboat Springs fault zone (Figure 2). This northwest-dipping, range- bounding normal fault extends along the east flank of the Williams Fork Mountains (Widman et al., 1998; Kirkham, 2004) and is located less than 1 km southwest of the Henderson Dam (Figures 2 and 3). The WFMF generally subparallels, and lies northeast of,the surface trace of the Laramide (late Cretaceous to Eocene) Williams Range thrust (Kellogg et al., 2011). Lying within the hanging wall of this older west-southwest-verging thrust,the WFMF generally uplifts early Proterozoic crystalline rocks in the mountains against Tertiary Troublesome Formation and Quaternary sediments in the valley(Kellogg et al.,2011). 12