turbidites. Cretaceous granitic intrusive activity was widespread in the Kahiltna terrane. Tertiary volcanic and sedimentary rocks, and Quaternary glacial deposits, developed over the older rocks. The Lake Clark fault, or a splay, probably lies within of the Pebble deposits and possibly much closer. The fault is a major right-lateral strike-slip crustal feature, considered to be a westward expression of the Castle Mountain fault. The actual ground trace of the fault and its splays are unknown in the Pebble area, due to extensive ground cover. A 2007 report indicates that magnitude 7.1 quakes occur on the fault on a 700-year cycle. The Lake Clark fault several hundred miles to the north is sub-parallel to the Denali fault and considered to be of similar nature. A magnitude 7.9 quake struck the Denali fault in 2002. The subduction zone of the Aleutian Trench lies approximately south of Pebble. This zone was the source of the 1964 Good Friday earthquake of magnitude 9.2. The Augustine Volcano, which lies 25 miles offshore, last erupted in 2006. The ore body A contiguous body of ore is known as Pebble West where mineralization locally extends to the surface and as Pebble East where it is deeply buried. Pebble holds mostly low-grade ore, requiring a large-scale operation to economically recover it. The Pebble deposit is hosted in porphyritic granodiorite to tonalite of Upper Cretaceous age intruded into deformed sedimentary rocks of the Jurassic to Cretaceous Kahiltna flysch terrane. The copper ore is a calc-alkali porphyry copper-gold-molybdenum deposit. The ore body extends from the surface to at least depth. In the western part of the orebody, mineralization occurs in a complex of several small granodiorite cupolas, diorite sills, older intrusions, breccias, and sediments. The western part of the deposit is locally exposed at the surface; thin gossans are developed and oxidation reaches in depth. The orebody extends eastward across a fault contact, at depth. East of the fault mineralization occurs in abundant sills and in the intruded sediments. Farther east, and deeper, the sills coalesce into a deeply buried granodiorite pluton. Mineralization and ore continue into the pluton. The eastern part of the deposit was eroded when it was exposed at the surface millions of years ago. It has since been buried by a thickening-to-the-east wedge of post-mineralization-age Tertiary sedimentary and volcanic sedimentary rocks. Mineralization at Pebble is aged from 90.4 ±0.6 MYA to 89.5 ±0.3 MYA. Metallic minerals