Some years ago, Roger Knights sent me a small sample of soil collected by MK Davis at what was believed to be the film site. Indeed the proponents are correct, it's not really even soil, it's more like fine, sharp, black gravel.
Yet this sample was collected nearly 40 years after the filming, so we really don't know if Davis' sample was representative of the conditions of 1967, especially considering that the creek was known to experience periodic and violent flooding.
I've always been amused how the proponents of the Skookum elk cast were quick to rationalize how there were no Sasquatch footprints leading up to the main impression by arguing that there were significant differences in the soil compliance within such a confined area, yet argue that the substrate of Bluff Creek circa '67 was uniformly rigid!
At the risk of repetition, it's certainly possible to impress a rigid prosthetic into non-compliant substrates with repeated stampings.
http://www.flickr.com/photos/matthetube/4818196349/
To be a bit boastful, I feel the inclusion of the mashed plants in the track was a nice little touch, as it demonstrates that there was no excavation...
I've personally attended several conferences where Jeff Meldrum gave presentations. He seems to have an ongoing feud with Dave Daegling to the effect that rigid prosthetics WORN by the hoaxer tend to dig into the substrate in an unnatural way. The toes tend to dig in too much. Clearly the centerpiece of Meldrum's argument is the particular track seen in one of the Laverty photos. I concede to Meldrum that indeed that track doesn't seem to have been made with a rigid prosthetic worn by a hoaxer. It's a strong enough claim that it deserves to be addressed specifically:
http://orgoneresearch.com/2009/10/19/bigfoots-mid-tarsal-break/
Here is what I suspect, but cannot prove:
1. The film is almost certainly a hoax.
2. That the tracks exhibiting a "mid-tarsal break" were probably made by the flexible feet of the guy wearing the suit.
3. Those tracks were made in a localized patch of compliant substrate, probably wet mud near the creek.
4. Additional tracks were made to create a convincingly long trackway using flat, rigid prosthetics in a non-compliant substrate like the kind I was given a sample of.
5. These rigid prosthetics were probably made of wood or concrete, rather than plaster of Paris, as I'm highly skeptical that plaster of Paris could survive the shock loads involved with repeated stampings.
6. Tracks made in non-compliant substrates could have excavated prior to impressioning. As far as I know, there was no fine plant matter in the creek bed like that seen in my front yard.
7. Additional human footprints alongside the alleged Sasquatch tracks are easily rationalized by claiming that curious people approached closely to examine the big tracks.
8. For what it's worth, in the test track from my front yard, my own footprint was made some years ago, when I weighed somewhere between 240 and 260 pounds.
9. If we accept that the casts Patterson displayed in the short film clip are from the Bluff Creek trackway, they most certainly model a track with a very flat and proportionately shallow impression, like that seen in my front yard test.