There has probably been about 8 km of crustal extension in a northwest-southeast direction across the Rio Grande rift near Albuquerque, New Mexico, since approximately 26 m.y. ago, giving an annual rate of about 0.3 mm/yr. This estimate is based on an interpretation that the normal faults bounding the graben decrease in dip downward and extend to a depth of about 10 to 15 km. Below that depth the crust is assumed to have undergone plastic deformation.

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