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<br />1ncompetent brecc1a (broken-up lava rock)assoc1ated w1th several very <br /> <br />1ncompetent ash depos1ts. These 1ncompetent un1ts tend to weather away <br /> <br /> <br />and underm1ne the surface bed of the mesa and the prom1nent c11ffs of the <br /> <br />source area are formed. <br /> <br />If the 1ncompetent beds had overla1n the competent ones 1n th1s <br /> <br /> <br />loca11ty, the Slumgul110n earthflow Drobably would never have formed. <br /> <br />PENNESON PARK, <br />A BLOCKED TRIBUTARY VALLEY <br /> <br />penneson Park can be seen from W1ndy Po1nt, just off the Slumgul110n <br /> <br /> <br />Pass road (Plate I). Th1s park or meadow 1s a blocked tr1butary valley <br /> <br /> <br />formed by the old Slumgul110n earthflow. Soon after the flow blocked the <br /> <br />valley, a small lake f111ed the area des1gnated on the map as Penneson <br /> <br /> <br />Park. The lake f111ed w1th sed1ments (sand, mud, clay, etc.), and the <br /> <br />result 1s Penneson Park, a relat1vely flat, marshy meadow, <br /> <br />Th1s park was blocked 1n much the same way as the Lake Pork of <br /> <br />the Gunn1son Valley was blocked. In both 1nstances a lake was formed, <br /> <br />and the only d1fference today 1s that Lake San Cr1stobal has not f111ed <br /> <br />with sedlments.................yet. <br /> <br />15 <br /> <br />c <br />c <br />C <br />-J <br />o <br />c;.J\ <br />