These grids constrain the loci of volcanic centers active in the last 5 million years. Informal names for these zones are listed below. Detailed information about each zone is provided in Smith and Luedke (1984).
| C | Cascade zone |
| S | Sevier rift |
| CL | Clear Lake locus |
| SG | St. George zone |
| SC | Santa Clara locus |
| E | Eagle locus |
| SS | Salton Sea rift |
| RMH | Rocky Mountain hinge zone |
| CZ | California zone |
| SF | San Francisco Mountains locus |
| WC | Western Cordilleran rift |
| V | Verde rift |
| B | Brothers zone |
| MR | Mogollon Rim lateral volcanic transgression |
| VV | Virgin Valley zone |
| J | Jemez zone |
| HR | Humboldt River zone |
| RG | Rio Grande rift |
| SR | Snake River zone |
| TC | Truth or Consequences zone |
| P | Pancake zone |
| H | Honeycomb Hills locus |
| LH | Leucite Hills locus |
The Western Cordilleran rift, Sevier rift, and Rio Grande rift are zones where the crust is undergoing east-west extension. Zones trending northeast and northwest are probably related to deeper tectonic control of melting in the mantle and may not be influenced by the upper-crust stress field.
Sources of Information
From Smith, R.L., and Luedke, R.G., 1984, Potentially active volcanic lineaments and loci in western conterminous United States, in Explosive Volcanism: Inception, Evolution, and hazards, National Academy Press, p. 47-66.
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