The Front Range was arched during the Paleozoic, as indicated by the sedimentary record on its flanks
<br />• (Lovering and Goddard, 1950, p. 29, 30) but this arching did not leave a recognizable record in the Idaho
<br />Springs district.
<br />During the Larunide orogeny in Late Cretaceous and early Tertiary time, the Front Range highland
<br />was arched and uplifted (Lovering and Goddard, 1950, p. 57-60). In the Idaho Springs district this arching was
<br />accompanied by the formation of the regional joint system and was accompanied or followed by the successive
<br />emplacement of nine varieties of porphyritic igneous rock - first, primarily in irregular plutons, thick dikes, and
<br />lenticular masses, and later, primarily in long narrow dikes. After most of the igneous activity but before the
<br />emplacement of the latest variety, a network of faults formed that trends east, east-northeast, and northeast:. The
<br />north-west-trending faults were then reactivated. Openings along the faults were filled with ore and gangue
<br />minerals, and, as indicated by the brecciation of minerals in many veins, fault movements continued during
<br />mineralization. This arching, jointing, and faulting evidently took place under compressive stresses that were
<br />oriented east-northeast. Late in the stage of mineralization, a few north-trending faults formed, and renewed
<br />movements occurred on some northwest-trending faults. The movement patterns indicate that tlus late faulting
<br />occurred under tensional stress oriented east-northeast.
<br />Since the Laramide disturbance the region has undergone deep erosion. The steep valley walls, narrow
<br />canyons, and fast-moving streams are indications that erosion continues today. The coarse alluvium in Clear
<br />Creek Canyon may, in part, be outwash from late Pleistocene valley glaciers that did not extend into the district.
<br />The continuous downhill movement of loose material is locally indicated by the colluviul creep debris sheets,
<br />though these, in part, may have formed in late Pleistocene time (Harrison and Wells, 1959, p. 26).
<br />(USGS Bulletin 1208, Economic Geology of the Idaho Springs District - Clear Creek and Gilpin
<br />Counties, Colorado,lvloench, Robert H. and Drake, Avery Ala, Jr., 1966).
<br />The only major, The oajor, identifiable fault know to exist in the area is the Idaho Springs Fault which is illustrated in USGS
<br />Bulletin 1208, Plate 2, Generalized Geologic Map and Sections of the Idaho Springs District Colorado attached to
<br />this Exhibit T.
<br />This fault is located 1,500' to the south of the proposed operation and does not impact the underlying geology.
<br />Detailed above in 6.4.20(8)(b) is a description of the vein and fracture systems that underlie this area and provide a
<br />hydraulic drainage connection to the Big Five Tunnel.
<br />6.4.20(8)(e)
<br />Detailed above in 6.4.20(8)(b) is a description of the vein and fracture systems that underlie this area and provide a
<br />hydraulic drainage connection to the Big Five Tunnel.
<br />Refer to USGS Bulletin 1208, Plate 3, Geologic Section Aloes the Big Five Tunnel Idaho Springs District,
<br />Colorado in the appendix of Exhibit C to see this connectivity.
<br />6.4.20(9)(a)
<br />The groundwater in this vicinity is unclassified, per the CO Division of Water Resources and is primarily considered
<br />surface water recharge .
<br />The poor, pre-existing quality of the groundwater in this mining district make it a poor choice for domestic water
<br />wells ... usually an attempt at drilling a well come up "dry" because the district is drained by the Big 5 and Argo
<br />Tunnels. Evidence of this is the existence of (1) domestic groundwater well downgradient of our proposed
<br />operation (see appendix of Exhibit. Q. Many residents just north of the operations and throughout the Virginia
<br />Canyon region actually haul water to cisterns for domestic use. The City of Idaho Springs constructed a water fill
<br />station at the west end of town to service this sort of customer. Central City has also constructed a similar station
<br />• near Russell Gulch.
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