The material we have seen so far is what formed the lower "strata" that creationists claim models the Grand Canyon.
It also forms a sad example of how creationists cannot bring themselves to tell the truth.
First note that the flow was much higher than the residual deposit.
Next, look at the amount of surface vegetation, tree bark and branches that were ground-up and added to the flow.
Saint Helens volcanic eruption both "proved" that the Grand Canyon was deposited and carved out in the year of Noah's flood, and of course that Noah's Flood even occurred. This will produce a well mixed combination of older volcanic deposits, and a smaller amount of fresh material introduced by the eruption.
Chief in their "proof" is this photo attributed to Steven Austin of the Institute for Creation Research. What this deposit will not be is well sorted by size, nor will the larger fraction be at all rounded.