Percolating water from seasonal rains and melting snow carries tons of gypsum, in solution, from the highlands at the north end of the basin into Lake Lucero. During much of the year, cloudless skies and warm dry winds evaporate Lake Lucero, and it shrinks to a crystal-encrusted marsh. Capillarity draws the gypsum-laden underground water to the surface; it, too, evaporates, depositing its burden of gypsum throughout the extensive “alkali flats.” The persistent southwest wind picks up the particles of gypsum and whirls them away, adding them to the gleaming white dunes, the accumulation of centuries. The best ways to see the dunes are by car and by foot. Along the drive that leads into the heart of the duneland are numbered posts that correspond to numbered paragraphs in the Monument’s informational folder. These paragraphs explain the features that are of particular significance. At pull-outs along the drive, park the car and walk among the dunes. [Illustration: Capulin Mountain National Monument] Capulin Mountain National Monument Capulin Mountain National Monument, in the northeast part of the state, is an area of geologic interest that presents still another aspect of the science of the earth. It contains the cone of an extinct volcano, one of the most symmetrical of the geologically recent cinder cones in the United States. Its conical form rises more than 1000 feet above its base. The irregular rim is about one mile in circumference, and the crater is about 415 feet in depth, as measured from the highest part of the rim. Some 40,000 people a year visit the Monument. The mountain consists chiefly of loose cinders, ash, and other rock debris of volcanic explosions. These materials were spewed out by a series of successive eruptions, probably of considerable duration. The coarse materials fell back around the vent, piling up to form the conical mound. Dust and other fine materials were carried away by the wind. After the eruptions, vegetation gained a foothold on the steep, unstable flanks of the cone, so that in time the slopes became stabilized. Geological studies indicate that the volcano probably was active about 7000 years ago. Capulin Mountain is of special interest, partly because it represents the last stages of a great period of volcanic activity that was widespread throughout western North America. Evidences of this older and more intense activity can be seen from the top of Capulin Mountain in the scores of other nearby volcanic hills and peaks. The largest of these is the Sierra Grande, an extinct volcano rising 4000 feet above the surrounding plain; it is ten miles to the southeast. Northwest of Capulin are a number of mesas that are capped with black lava, the largest of which are Barella, Raton, and Johnson. Fishers Peak, south of Trinidad, Colorado, is on a similar mesa. The famous Spanish Peaks, northwest of Trinidad, are a pair of extinct volcanoes.