Gravity and stratigraphic analyses indicate that a trough was created and subsided probably more than a kilometre during the interval 25 to 22 m.y. B.P. (late Oligocene; Berggren, 1972) in the Candelaria Hills, Nevada (Fig. 1). We interpret the trough, here named the “Candelaria trough”, to have been the result of extensional faulting. The implication is that extensional tectonics apparently existed in the Candelaria region earlier than at most places in the Great Basin where onset of block faulting is thought to have been at about 17 m.y. B.P. (McKee and Noble, 1974).
This paper presents gravity data and interpretations of the structure of the Candelaria trough. Models include a three-dimensional approximation of the whole trough and four profiles which give improved resolution of the configuration of the locally steep southern flank of the trough. Data are also given on Cenozoic structures within the trough (folds, normal and. decollement faults) with which we interpret some aspects of trough formation. The Candelaria mining district (Page, 1959) occurs in pre-Tertiary rock at and near the southern wall of the Candelaria trough. Ventures in exploration for continuations of the ore-bearing terrane below the Cenozoic cover of the trough may find models of this paper of some benefit.