We examine the characteristics of 3-day total extreme precipitation in the Western United States. Coherent seasonal spatial patterns of timing and magnitude are evident in the data, motivating a seasonally based analysis. Using a clustering method that is consistent with extreme value theory (EVT), we identify coherent regions for extremes that vary seasonally. Based on storm backtrack analysis, we are able to demonstrate unique moisture sources and dominant moisture pathways for each spatial region. In the winter the Pacific ocean is the dominant moisture source across the west, but in other seasons the Gulf of Mexico, the Gulf of California, and the land surface over the Midwestern US play an important role. We found the El Nino Southern Oscillation (ENSO) to not have a strong impact on dominant moisture delivery pathways or moisture sources. The frequency of extremes under ENSO is spatially coherent and seasonally dependent with certain regions tending to have more (less) extreme events in El Nino (La Nina) conditions.