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Dissolution ancl flow of Pennsylvanian evaporitic rocks in west-central Colo~ldo created the Carbondale Collapse Center, :I 450 mi2 structural clepression w~th bout 4,000 ft of vertical collapse clurlng the late Cenozoic. 'I'his paper describes ev~dence of collapse 111 the lower Roaring Fork River valley. Both the lateral extent mcl mount of vertical collapse is constralnecl by cleformecl upper Cenozoic volcanic rocks that have been correlated using held mapping, 40~r/39~r geochronology, geochemistry, ancl paleomagnetism. 'The C:irbonclale Collapse Center is one of at least two contiguous areas that have experienced major evaporite tectonism during the late Cenozoic. I-listoric sinkholes, cleformecl Holocene deposits, and moclern high-salinity loacls in the rivers and thermal springs indicate the collapse process continues toclay. Flow of evaporitic rocks is an important element in the collapse process. ancl cluring initial stages of colhpse it was probably the psiniary causative mechanism. Dissolution, however, is the ultimate means by which ev:~porite is removecl from the collapse area. As the Roaring Fork liiver began to rapiclly clowncut through a broacl volcanic plateau during the late Miocene, the unclerlying evaporite beck were subjected to differential overburclen pressures. 'l'he evaporitic rocks flowed from beneath the uplancl areas where overburclen pressures remained high, toward the Roaring Fork liiver Valley where the pressures were much lower Along the valley the evapori~ic rocks rose upwarcl, sometimes :IS cliapirs, forming or enh:lncing :I valley anticline in beclrock ancl locdly upwarping 1)leistocene terraces. Wherever the ev:p orites encounterecl relatively fresh ground water, they were clissolvecl, forming unclergrouncl voicls Into which overlying lxclrock and surficial clepos~ts subsiclecl. The saline grouncl water eventually clischargecl to streams and rivers through thermal sprlngs ancl by seepage into :~lluvial aquifers.
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