“The flood peak passed through Denver during the night, and the immediate crisis was over by morning; but those in the inundated areas were faced with a Herculean task. The light of day revealed the nature of the destruction—mud in every nook and cranny, soggy merchandise, warped bowling alleys, drowned animals, the loss of irreplaceable possessions, to name a few types. The colossal cleanup job, which would take months, began.” Hydrogeological studies by the U. S. Geological Survey and Corps of Engineers give knowledgeable estimates of flood danger for different populated areas of the state, and recommend that homes, roads, and other structures be placed above likely flood levels. GLOSSARY Alluvial fan. A cone-shaped mass of sediment built by rivers or streams as they issue from mountains onto more level ground. Alluvium. Stream deposits formed in recent geologic time, composed of sand, gravel, and stones. Ammonite. One of a large group of extinct mollusks related to the living chambered _Nautilus_. Ammonite shells, usually cone-shaped or coiled, are divided into many chambers by crenellated septa. Angular unconformity. A surface separating tilted or folded layers of rock from overlying less disturbed layers. Anticline. An upward fold or elongated arch in rock layers. Aquifer. A rock layer that is water-bearing. Artesian water. Groundwater that is under sufficient pressure to rise above the level at which it is encountered in a well. It does not necessarily rise completely to the surface. Basalt. An extrusive igneous rock, fine-grained and dark colored, composed mainly of calcium-rich feldspar and the black mineral pyroxene. Basement. A name commonly applied to metamorphic or igneous rocks underlying the sedimentary rock layers. Batholith. A large body of intrusive igneous rock, 40 square miles or more in outcrop area, which extends downward to an unknown depth. Bedrock. The solid rock which underlies soil, sand, clay, or other loose surface material. Belemnite. The cigar-shaped internal shell of an extinct marine mollusk similar to a squid. Brachiopod. One of a large group of marine shelled animals having two unequal, bilaterally symmetrical shells. Bryozoa. A large group of tiny colonial marine animals that secrete calcareous or horny coverings in a great variety of shapes. Caldera. A large basin-shaped depression caused by explosion or collapse around a volcanic center. Cassiterite. A heavy, brown to brownish black mineral composed of tin and oxygen (SnO₂) that is an ore of tin. Cephalopod. A marine mollusk with a head surrounded by tentacles. Squids and octupuses belong to this group, as do fossil forms having straight or coiled shells divided into numerous interior chambers. Chalcopyrite. A reddish-gold colored ore of copper (CuFeS₂).