Heart Mountain and South Fork fault systems Architecture and evolution of the collapse of an Eocene volcanic system, northwest Wyoming

Thanks to Anders et al. (this volume) for their attention to the legacy of the late Ed Beutner, and to his and my recent Rocky Mountain Geology paper (Beutner and Hauge, 2009). I make no claim of being able to reply to their comment as aptly as Ed would have, but here I'll try to represent my own perspective (and Ed's, as I recall it) on their remarks. Beutner and Hauge (2009) made a case for an early, noncatastrophic phase of displacement along the Heart Mountain (HM) detachment, followed by final catastrophic emplacement of the allochthon. Anders et al. (this volume) argue that this noncatastrophic phase is not supported by the evidence, and they cite both data (calcite twinning; radiometric ages) and models (Aharonov and Anders, 2006) in support of this claim. The models of Aharonov and Anders (2006) and Beutner and Hauge (2009) are fundamentally incompatible because the Aharonov and Anders model requires that the Paleozoic strata of the future allochthon were intact and able to confine pressure that triggered catastrophic failure. In the Beutner and Hauge model, significant extension of the HM allochthon had already taken place when catastrophic failure was triggered. Both models have weaknesses. To varying degrees they require initial conditions that are improbable, explain away conflicting data, inadequately confront alternative models, and make predictions that are not borne out by available data. The resolution of the problems of the initiation, maintenance, and rate of displacement of the HM allochthon has been hampered by the vast scale, rugged terrain, and concealment by younger strata that have made observations difficult. As it has for over a century, the problem remains unresolved. ### Issues Surrounding Beutner and Hauge's (2009) Comments on Aharonov and Anders (2006) The following paragraphs respond directly to the comments of Anders et al. (this volume) in the context of the two competing models. Beutner and Hauge (2009) …