At first I thought it was a comb.
Then I saw that there were nails rather than bristles.
The other side appears to be stone.
I live in Northern California and found it on a trail leading to Stinson Beach.
The only other thing I could think of is some sort of wool card, never seen one like it but theres a lot of things made through every era that tried to re-invent the wheel. I like it whatever it is
These are my thoughts I have seen curry combs that look like that although none ever had nails, also when I was a teenager I used a trash picker upper that had a square bottom with nails in it, stab the trash then remove it although I can't see where the pole would have attached to yours, unless it fit in something that encased it thus no attaching points.This was 30 yrs ago for the trash grabber now they have the tong style.Hopefully this helps in your I.D.
it is a military type civil war to rev war era type of horse "body" brush -- the teeth are often copper or iron --the body was made of pewter or lead * ==I have one from a civil war camp that had horses to pull their cannons -- I found it along with a hoof pick , a farriers hammer., and a mane / tail brush and other horse care items at the site.--it was used to "lightly" brush down the horse's body to remove sweat , mud and small burrs and such that might stick to the horse hair / hide -- civilian ones were often of wood body and stiff pig hair bristles . (like modern one of today).
I agree with Creskol; it looks like a flower frog. Generally 'most' antique flax combs and curry combs had straight needles, meaning each bristle is the same size; whereas flower frogs have a chiseled point at the end that looks like a nail.
My mother used to be into the Japanese flower arranging and used frogs a lot. However, the difference in your find vs. hers were hers were flat on the bottom. It could be an illusion, but it appears yours has a rounded bottom.