Just drive out into the country a few miles and find a gravel road. Scoop up a few buckets of dirt and stones. Use some 1/8" screen to filter out the large rock and pebbles. if it is too big the hens won't pick it up. Or find a small clear running stream and scoop up some fine pebbles.
I'd steer clear of granite, lots of toxic heavy metals found in granite.
I'd steer clear of granite, lots of toxic heavy metals found in granite.
