The possibility of relatively large intact folds has intrigued Nevada exploration geologists since the 1950's. Surface closures in Paleozoic and Mesozoic rocks have led several companies to drill in hopes of finding a hydrocarbon accumulation which has not been breached and destroyed by the ravages of Tertiary extension.

Large-scale, broad and open folds of Paleozoic through Cenozoic, and dominantly Mesozoic ages, exist in the Pinon and Adobe Ranges, the Simpson Park, Cortez, Diamond and Fish Creek Mountains, Buck Mountain-Bald Mountain, Pancake, Butte, Pequop, and Leach Mountains, and in the Currie Hills area. These folds are discussed in some detail in the Structural Setting portion of this volume.

A systematic analysis of folding focusing on factors such as orientation, period, amplitude, continuity, and origin is necessary to understand and predict the occurrence of these folds in adjacent basins. Although folds have been mapped within several ranges, the lateral and vertical continuation of these folds is uncertain. In many cases these folds appear to be related to both high-angle and low-angle normal faults and may not continue with depth. An interpretation of well penetration in the Summit Spring anticline in the Butte Mountains for instance, indicates that this Mesozoic fold did not continue to depth (Douglass, 1960).

Thermal reconstructions suggest that Tertiary thermal events are responsible for known hydrocarbon accumulations in northeastern Nevada. Microcline paleothermometry, done for this evaluation, shows that sections in the ranges have not seen Tertiary thermal events related to burial beneath basin fill. This suggests that exposures in the present ranges have not seen adequate thermal conditions to generate hydrocarbons during the Tertiary. Thus, Mesozoic folds in the ranges would have to rely on preserved hydrocarbons generated and migrated during the Paleozoic or Mesozoic. In the adjacent basins, it may be possible to generate oil during the Tertiary from Paleozoic source rocks contained within preserved segments of these Mesozoic folds.

Most of these folds have been broken by high-angle faults with small to moderate displacements in the ranges. In the adjacent basins, these folds are commonly segmented by both major and minor high-angle faults. The most attractive Mesozoic folds would be in basins with a low relative intensity of Cenozoic deformation. For instance, folds in the Butte Mountains area may be more intact than those in the Fish Creek or Pancake Ranges.