How to collect and prepare non-toxic earth paints

I just drove from Jacksonville, OR to the Redwoods in Northern CA and found many beautiful oranges, reds and deep yellows along the side of the road. Good locations to find pigments are road cuts, quarries (which often reveal strata of several different colored earths), eroded areas, banks of rivers or streams, or construction sites. The mountains or along the coast of Oregon are rich with iron oxide pigments. Bad locations would be open fields or areas with crops or dense growth.
I just stuck a trowel and some baggies in the car and dug up samples along the way. It’s important to label really well with exact location so you can come back to get more in the future. Look for soil as free as possible of humus (organic matter), rocks and sand- you want mostly clay.
Washing the soil: This is not an essential step unless it’s filled with a lot of foreign matter….Mix earth with water to make a “slurry”. Allow to settle for hours or days. Sand and heavy materials go to the bottom- humus floats to top. Remove floating matter on top and siphon out water with syringe.
Drying Pigments: Spread on newspaper, burlap, fabric and put in sun or studio to dry
Grinding: Sift thru a flour sifter or screen to remove particles of humus or gravel; then grind in a mortar and pestle. Sift and grind again if needed.
Making your own oil paint could not be any easier. It takes about 60 seconds really. On a glass or enamel surface, place a pile of dry pigment (a tablespoon or two to start). Add walnut oil or walnut alkyd medium (which makes the paint dry faster) by drops, a little goes a long way. Use a sturdy rounded, flat palette knife to work the oil into the pigment until it is the proper consistency, continually bringing the outside of the paste towards the center. You can also use a glass muller to ensure that every particle is coated with oil (see picture below) but it’s not totally necessary. This paint is then used immediately from your palette. You can use more oil to make the paint thinner.