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<br />.. <br /> <br />14 <br /> <br />The cliffs that bound the eastern edge of the source area are <br /> <br />alternating lava flows and ash deposits. All of these units have relative <br /> <br />o <br />o <br />o <br />-J <br /><:;;> <br />M" <br /> <br />strengths with relation to their ability to resist weathering. This <br /> <br /> <br />strength is called competency. With beds having different competencies. <br /> <br /> <br />the effect of weathering has different results. For example. if a tougher <br /> <br /> <br />or more competent bed underlies a less competent bed. the uppermost bed <br /> <br /> <br />will simply weather away. However, if the reverse is true and the more <br /> <br /> <br />oompetent bed overlies a less competent one, a cliff will result. <br /> <br />The competent bed will resist <br /> <br />weathering and form a bluff or mesa. <br /> <br />The underlying less competent bed <br /> <br />will tend to weather much faster, <br />the result being the undermining of <br /> <br />the competent bed. <br /> <br />The western edge of Mesa Seco <br /> <br /> <br />'/ <br />'/ Resis4aV'\1- (~"der) <br />/ {;::Lova /F\o...:> /1 /I~ <br />~" .1<<:'1{1I<<<f.,.,. <br />. "Less Re:;,S-\-o'n-\ ....:;' <br />,;;: (so#u- ): r ^ 5"" .lInd..:; <br />,.,.. 'I. '" ".... . '..'"..1 <br />;:, .,' \\B~ec.c.\ l! _, I " t <br />- ... "'..... i'...... , . _, I \ l .... <br />... .., ". ...... ...." ,"... <br />.. '. - ...... ".. '--'~ .... . <br />....' ---- <br />~..~~ <br />.. ...., <br />. . t. . <br /> <br /> <br />consists of a series of volcanic beds which have different competencies. <br /> <br />-. <br /> <br />The uppermost bed in this series, which forms the cliff rim of Mesa <br /> <br /> <br />Seco, is a very durable .lava flow (quartz latite) which resists weathering <br /> <br /> <br />and forms the surface of the mesa. Just beneath this bed is a relatively <br />