New Mexico produced 26.7 million st of coal in 1997. Two-thirds of this tonnage is delivered to three electrical generating stations in New Mexico. All but a small portion of the remaining production is shipped by rail to generating stations in Arizona. New Mexico coals are high in ash content, from 13-27%, creating a significant amount of coal combustion byproducts most, of which is fly ash. The use of fly ash from New Mexico is significant (1.59 million st), about 44% of the total fly-ash production (3.59 million st) in 1997. New Mexico coals produce Class F fly ash with a high silica and low calcium content. These characteristics make New Mexico fly ash a beneficial admixture for portland cement concrete particularly in the Southwest where alkali-silica reactivity is a problem because of the type of aggregate available.