The Moroni Formation is an Eocene-Oligocene volcanic-sedimentary unit that is exposed in central Utah in the Cedar Hills and north to Salt Creek Canyon (SCC) and Thistle. The source of the Moroni Formation has not been resolved with arguments for either a local source or a source in the East Tintic complex. Investigations in SCC show that the Moroni Formation has multiple sources with the East Tintic complex being just one.
The Moroni Formation in SCC consists of a volcaniclastic sequence with associated air fall tuffs, a series of lava flows, and a large (300 ft wide) trachyte dike. The volcaniclastic sequence is informally divided into five members based on clast composition and field relations. Member 1 is a series of mass flow deposits composed of angular blocks (up to 8 ft) of porphyritic andesite with rare intercalated tuff beds that were deposited near a stratovolcano. Member 2 is composed of a basal layer of trachyte blocks (up to 8 ft) overlain by lapilli tuff, and is interpreted as a block-and-ash flow. Member 3 is composed of a series of mass flow deposits that grade into tuffaceous sandstones with channel conglomerates and numerous ash fall tuff beds, and is interpreted as an alluvial fan deposit. Clasts consist of trachyte (up to 10 ft), andesite, and minor quartzite and limestone. This member also includes a 60 ft thick series of lava flows and agglomerates. The fourth member is composed of tuffaceous sandstones and channel fill conglomerates with clasts of welded tuffs, andesites, and rare quartzite. Member 5 is lithologically and petrographically identical to member 1. The two are differentiated based on there geographic occurrence. Member 1 is located in SCC while member 5 is located high on the flanks of Mt. Nebo. Since there are not any intrusions recognized on Mt. Nebo members 1 and 5 must have been derived from a source elsewhere. The closest and most likely source is the East Tintic complex which is a few miles to the west. However, the East Tintic complex is at a significantly lower elevation than Mt. Nebo currently. It is postulated that the current topographic discrepancy is due to extension that occurred after deposition of member 1 and 5. Therefore, a large mountain range was formed by Sevier compression to the west of Mt Nebo where volcanism was active producing mass flows that were deposited on Mt. Nebo and in SCC. The block-and-ash flow was derived locally from the trachyte dike which was emplaced and extruded as a viscous mass forming a lava dome, which collapsed producing member 2. Member 3 was deposited in a graben during pre-Basin and Range extension. The material clasts were derived locally but the volcanic material was derived from an unknown volcanic source. The clasts in member 4 are very similar to the ashflow tuff in the Cedar Hills indicating that the clasts were derived from there.