Alluvium (from the Latin, alluvius, from alluere, "to wash against") is loose, unconsolidated (not cemented together into a solid rock) soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it would be called an alluvial deposit.
Costa Rica (i/ˌkoʊstə ˈriːkə/, meaning "rich coast" in Spanish), officially the Republic of Costa Rica (Spanish: Costa Rica or República de Costa Rica, pronounced: [reˈpuβlika ðe ˈkosta ˈrika]), is a country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west, and the Caribbean Sea to the east.