1-Homogenous gravel, here illustrated by gravel beneath the Poudre River, is essentially uniform and can be sampled without regard to stratigraphic level. Homogenous gravel is probably more typical of tributary streams near the mountains. 2-Stratified gravel, here illustrated by gravel beneath the South Platte, is strongly segregated by particle size.
Stratigraphic units are traceable for miles beneath the South Platte River north of Denver.
Stratigraphic level must be known to sample effectively. Stratigraphic variation in particle size may affect mining procedure. Stratified gravel is probably typical of trunk streams.