2018-04-02_REVISION - M1977342

• Permit No: M1977342
• IBM Index Class Name: Revision
• Doc Date: 4/2/2018
• Doc Name: Adequacy Review Response
• From: Climax Molybdenum
• To: DRMS
• Type & Sequence: TR29
• Email Name: PSH
• Email Name: WHE
• Media Type: D
• Archive: No

This complex group of several overlapping and intersecting faults lies at the southern
end of the Mosquito Range and the northeastern end of the upper Arkansas Valley
(Unruh,et a],1993;Widdmann et al.1998}As originally mapped,and included in
the USGS database,this fault system includes the Union fault,which was alternatively
shown as intersecting and possibly cutting the Mosquito fault(Unruh et al.,1993)or
merging with the Mosquito fault as more recently mapped by Bohannon and Ruleman,
2013). Due to a lack of slip rate data,we assumed slip rates similar to the Mosquito
fault.Due to the complex geometry with multiple overlapping and intersecting faults
with no main associated basin,steeper dips were assumed.In his review of the new
0.01(0.2) LIDAR data and a brief field reconnaissance for a proposed dam site,R.Kirkham
Northeastern 6.8(0.2) 501 W(0.2) 0.03(0.6) (GeoLogic Soutions,pers.Comm.,2015)observed that the Union fault appears to have
Boundary fault 7.1(0.6) 70P W(0.6) 0.17(02) Unruh et al.(1993);Widmann et the best geomorphic expression of all the fault traces of the Northeastern Boundary
system 57/2309 Independent 1.0 1.0 1 48 N/R? 7.4 02 901 0.2 WM:0.05 al. 1998•Wong et al. 200 system.
Segmentation model after Ostenaa et al.(1981�Unruh et al.(1992)and Lettis et al.
(1996} On the southern segment,Ostenaa et al.(1981)originally reported evidence
for 6 events occurring since 100-150 ka,then revised this interpretation to 2 or 3 events
since 130-160 ka.Slip rates based on 2 to 3.7 in of vertical offset on 15 to 40 ka
6.7(0.2) 0.01(03) deposits,and rates of 0.05 to 0.1 mm/yr estimated from offset Bull Lake deposits
7.0(0.6) 0.05(0.4) Ostensa et al.(1981);Widmann (Ostenaa and Nelson,2002).Specific slip rate data for the northern segment is lacking,
Sawatch fault Segmented(0.8) 7.3(0.2) 35"E(02) 0.2(0.3) et al.(1999);Nelson et at.(1984); but based on the evidence for no offset of Pinedsle deposits and a poorer geomorphic
(Q56/2308a and Northern Section 34 50'E(0.6) WM:0.08 Nelson and Shroba(1998); expression(Ostenaa and Nelson,2002;Shrubs et al.,2014�we assumed slip rates less
2308b) 1.0 N 65°E 02 Ostensa and Nelson 2002 than the southern Sawatch segment,but slightly more than the Mosquito fault.
Recurrence
Intervals(0.5):
10(0.2)
25(0.3)
50(0.3)
140(0.2)
Slip Rate(0.5):
0.01(02)
0.07(03)
0.13(03)
6.8(0.2) 0.3(0.2)
Southern Segment 41 7.1(0.6) WM:0.12
7.4(0.2)1
0.01(02)
0.07(03)
7.1(02) 0.13(03)
7.4(0.6) 0.3(0.2)
Un mented 02 84 7.7(0.2) WM:0.12
This series of late Cenozoic but poorly understood north to northwesterly striking
6.9(0.2) 5W E faults offset the Tertiary Browns Park Formation(Snyder,1980�but they are not
72(0.6) 70°E known to offset Quaternary deposits(Snyder,1990;Kirkham and Rogers,1981}
Unsegmented(0.5) 63 7.5(0.2) 90, Therefore,they were not included in the Quaternary fault compilation of Widmann et
al.(1998)or in the USGS Quaternary fault database. However,because these faults
are not wel"tudied and do appear to have significant Tertiary offset,we did include
Steamboat Springs 6.7(0.2) 5W E 0.006(02) them in this analysis,but with a low probability of activity. As little is known about
fault zone(fault no. Segmented(0.5) 7.0(0.6) 70°E 0.02(0.6) rates of activity,we assumed similar slip rates to the nearby Greenhorn Mountain
43 of IGrkham and Northern Segment 36 73(02) 90" 0.1(0.2) Kirkham and Rogers(1981); fault.Due to the structural setting,somewhat linear trace geometry and no associated
Rogers,1981 0.2 1 N WM:0.03 Sn der 1980 well defined basin,we assumed steeper dips.
6.7(01)
W W
7.0(0.6) 70°W
Southern Segment 34 7.3(01 90°