Joint Patterns and Relationships of the Eastern Sierra Nevada Batholith, California.

The Sierra Nevada Batholith is composed of igneous rock that cooled beneath the surface after magma intruded the crust, and is now exposed over most of the east central part of California. An area of particular interest is just East of Eldorado National Forest, approximately 20 miles south of Lake Tahoe. Examining this area in Google Earth reveals an abundance of megalineaments (crustal-scale fractures measured in kilometers) that frame domains with different internal fracture patterns. On an outcrop scale, joints scar most of the exposures and are heavily clustered, with dominant orientations prevalent by domain. Joint orientation was controlled by the local stresses, and joint truncations indicate age relationships, with the truncated joints forming after the truncating joints. By analyzing these relationships, conclusions can be drawn in regards to the history of the causative stress fields, reactivation, and overall impact of fractures on domain development. Hundreds of fractures from a study area of ≈ 72 mi2 with 3 large domains and 22 individual sites (outcrop-scale fracture orientations), were traced in Adobe Illustrator and orientations computed. Each of the domains individually display strong orthogonal orientations. There are various stresses that could form orthogonal patterns within this area, such as stresses from the cooling of the batholith, regional stresses, and local stresses. The Sierra Nevada Batholith cooled at depth and along an active tectonic margin, as a result, determination of these specific stresses require in-field investigation