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.

The term "alluvium" is not typically used in situations where the formation of the sediment can clearly be attributed to another geologic process that is well described. This includes (but is not limited to): lake sediments (lacustrine), river sediments (fluvial), or glacially-derived sediments (glacial till). Sediments that are formed and/or deposited in a perennial stream or river are typically 'not' referred to as alluvial.

Most, if not all, alluvium is very young (Quaternary in age), and is often referred to as "cover" because these sediments obscure the underlying bedrock. Most sedimentary material that fills a basin ("basin fill") that is not lithified is typically lumped together in the term alluvial.

Jim Sanborn (born Herbert James Sanborn Jr., 1945 in Washington, D.C.) is an American sculptor. He is best known for creating the encrypted Kryptos sculpture at CIA headquarters in Langley, Virginia.

Sanborn's father was the head of exhibitions at the Library of Congress, and his mother was a concert pianist and photo researcher. He grew up in Alexandria and Arlington, Virginia, attending JEB Stuart High School in Fairfax, and then attended Randolph-Macon College, receiving a degree in paleontology, fine arts, and social anthropology in 1968, followed by a Master of Fine Arts degree in sculpture from the Pratt Institute in 1971. He taught at Montgomery College in Rockville, Maryland, and then for nine years was the artist-in-residence at Glen Echo Park.

His artwork has been displayed at High Museum of Art, the Los Angeles County Museum of Art, the Corcoran Gallery of Art, and the Hirshhorn Museum and Sculpture Garden. He has created sculptural works for the Massachusetts Institute of Technology, the Central Intelligence Agency, and the National Oceanic and Atmospheric Administration. Themes in his work have included "making the invisible visible", with many sculptures focusing on topics such as magnetism, the coriolis effect, secret messages, and mysteries of atomic reactions.