For me, if the rocks are large enough to get generally solid foot and/or hand holds, it's talus.

If they're small enough that I have to use gaiters to keep them out of my boots, it's scree.

Some slopes are a combination of both.

Boulders > Talus > Rubble > Scree

Getting hit by a single piece of talus will likey result in injury.
Getting hit by a single piece of scree will likely do no harm.

Think of scree as being the consistency of kitty-litter.
Think of Talus as being like the armour rock on jetties or the banks of storm channels.

http://www.summitpost.org/columbine-peak/150563

Here eons of wind, rain, snow, ice, snow avalanches, earthquakes, water freezing in cracks, have brought down all matter of granite rock sizes on this face. There really is much more finer scree than talus but it is mostly hidden as large talus tends to rest on the top of finer rocks so it appears to be mostly larger talus.

(mouse click to expand)


Of course as large rocks break off the steep face and fall, they can only pile up atop the top layer of large boulders. The smaller rocks however, especially the finer debris after falling can fit between the large talus boulders so given rain and time ends up unseen. Large boulders falling onto the base of the monolithic steep areas have considerable force so are unlikely to stop there thus continue beyond into the larger boulders where they meet their talus buddies. Thus right at the base of the monolithic rock is mostly scree with a few scattered larger boulders.

Below the scree far enough below is likely bedrock. Water seeping through all the rock makes it down to that mostly impervious bedrock then flows along it sometimes forming sheets of ice. The heavy piles of rock atop that base layer of water and ice tends to slide so over time the masses of rock moves away from the monolithic face down the slope. Where a knee in the bedrock gradient probably increases at frame lower left corner, the rock glacier exposes a steep scree face. For we experienced climbing about in such areas of the Sierra, some of the most unpleasantly unstable rock only a fool would gamble playing on. But then after looking at all the much more interesting ways to climb up this face on the monolithic who would bother to anyway?

Sam Henie wrote:Sorry to butt in here but to me Mt Shasta kind of looks like a volcano, which if so would infact hold not Talus, not hold Scree but instead hold Scoria? I maybe wrong here, please correct me if so.

Some of it may be scoria but a great deal of the mountain is composed of andesite and dacite, which is pretty tough stuff compared to cinders. Some of that rock is in the Mud Creek Canyon area, as well ash and other things. Mud Creek Canyon is believed to be the oldest exposed part of Mount Shasta, a remnant of earlier iterations of the mountain. Consequently, there is a lot of different stuff in the area, sort of a big rock concoction. Here is a larger picture to get a sense of the larger area:

Scoria is not a size description. Think of it as basaltic pumice.

Sam Henie wrote:Scoria is just like scree but looks slightly diffrent.

No. This is fairly good:
http://en.wikipedia.org/wiki/Scoria

Scree can be made out of any rock type.

Talus, 10-foot boulders, big solid mountain ledges, and scree can be made out of scoria.

Scoria refers to the "bubbly" (vesicular) nature of volcanic rock with approximately basaltic chemical composition.