In the foregoing outline of the structural history of the Grass Valley intrusive the vein fractures are regarded as elements of the internal tectonics of the intrusive body itself. They originated in an early stage of the structural development of the region, and are equivalent to the marginal thrusts observed in the Yose-mite and along the Mother Lode system. As such, the vein fractures are of local origin, since they are entirely restricted to the neighborhood of intrusive contacts. As the area of consolidation within the Sierra Nevada batholith increased, larger units were affected by tectonic stresses, and joints were formed which belong to a system of regional extent. As this system has been observed over an area of at least 7500 square miles, its regional character seems proven. Basic dikes and aplites follow the crossing system, and thus indicate that the earliest crossings were formed when magma to fill them was still available. Both fissure systems repeatedly served for adjustment of later stresses, as can be proved by relative mutual displacements and by the repeated fracturing and renewed deposition of quartz within the vein fissures. It is probable that these later stresses were regional in character.
