The Yucatan crustal block, once part of the southern margin of North America, was integrated within the Central American assembly during Late Mesozoic. The oldest rocks of Belize crop out in the Maya Mountains of central Belize, and consist mainly of Paleozoic crystalline rocks (Silurian-Devonian granitic plutons). Also in the Maya Mountain area are volcanics and meta-sediments of the outcropping Carboniferous-Permian Santa Rosa group. In northern Belize, the surficial, coastal plain Mesozoic-Cenozoic stratigraphic succession includes the Triassic-Jurassic Margaret Creek formation (red beds), Upper Cretaceous Barton Creek formation (limestone), Albion formation (K-Pg ejecta incluidng diamictites), Lower Cenozoic El Cayo group and Doubloon Bank formation (limestones and chert), Red Bank group (clays) and Iguana Creek formation (boulder beds), and the Upper Cenozoic Orange Walk group (sands and marls). Numerous Belize caves and caverns, which likely formed during an intensive episode of erosion during an Early Cenozoic uplift, are common in the foothills of the Maya Mountains. These caves and caverns, including a zone of tower karst, are situated mainly within the Barton Creek formation. In southern Belize, a strike-slip basin (Belize basin) possesses surficial stratigraphy that includes the Cretaceous Coban and Campur formations (limestones), the Lower Cenozoic Toledo formation (deep water clastics), and the Belize formation (limestones). The Maya made practical use of their local geologic environment, as noted in the following examples. Limestone, a common bedrock in many areas of northern Belize, was used by the Maya for substantial construction. Sascab, a saprolitic weathering product of limestone, is common across northern Belize, and was used by the Maya for mortar and other everyday purposes. Chert, most common in the Doubloon Bank formation of northern Belize and in some gravel deposits atop the Red Bank group and within the Iguana Creek formation of northwestern Belize, was used by the Maya for tools, sharps, and eccentric carvings. Clays, from caves and caverns and surficial stratigraphic units like the Red Bank and Orange Walk groups, were used for ceramics. Slate from the Santa Rosa group in the Maya Mountains was used for slate carvings and etchings. Belize's extensive cave systems were integral to Mayan underworld belief systems, and the related cenotes (sinkholes) were key sources for fresh water in the Mayan world.