Spruce root is used as a basic weaving material (the weft) to hold together the sticks (the warp). Most often in Klamath River baskets, the root is overlaid with another more colorful material, but it's the root that gives the basket its strength. (Some basket weavers may also use willow root.)
Root is most often used on tight-weave baskets (some are even used for cooking!). The photo below shows a traditional Karuk tobacco basket which I made two years ago.
These were/are utilitarian baskets and as such were often not decorated at all. Most of what you see on this basket is spruce root, only overlaid with the lighter colored bear grass to form a simple but inconspicuous design.
You will also see larger pieces of root, after being split into a flatter form, used for wrapping on things like baby rattles and baby baskets.
As with all of our basket materials, it's not simply a matter of gathering the spruce root. The next step is to process the roots into more usable materials.