You have to leach them, as I recall, from cub scouts.
Indeed!
Pulverize them, then sprinkle the fine powder on the fine-grain sand of a river bank. Then sprinkle water droplets onto the powder (using a small twig as an aspergillum). This is a time-consuming process! The powder will clump. Carefully remove finger-sized clumps from the river bank, rinse, and put into basket. Repeat.
Some small amount of very fine-grain sand will inevitably remain in the mush. This is why the teeth of the Indians was invariably ground down considerably by the time they reached their 40s.
I did this once when I was a kid in Sonoma County in the 1960s. I was expecting something tasty. Tried adding processed white sugar, cinnamon, milk, etc. - to no avail. Couldn't get more than two spoon-fulls down. Today, even as an adult, I would venture to say that, properly prepared, this mush would be barely palatable. However, if you are an Indian living on the brink of starvation, it would be delicious.
Regards,