Which specific type of soil is described as having a gravel-sand mix?

The designation GW refers to well-graded gravel. In soil classification, particularly within the Unified Soil Classification System (USCS), well-graded soils have a good distribution of particle sizes, which provides better compaction and drainage characteristics. When a soil sample contains gravel mixed with sand, it typically falls into this category, especially when the proportions are balanced to maintain the well-graded nature.

The distinction in the other classifications is significant; for instance, GP stands for poorly graded gravel, which lacks the same mixture balance and effective range of particle sizes. SM-SC designates a silty or clayey sand, which does not accurately capture the gravel-sand mix. Lastly, ML indicates silt, which is entirely different from a gravel-sand composition. Thus, GW is indeed the most appropriate answer when identifying a soil characterized by a gravel-sand mix.