I would agree with
@Phil Coffins on both points.
I found several "Riddles" in
The Database of USA Gunmakers. I think the one that interests us in this case would be this one:
RIDDLE — Low and medium quality commercial percussion locks, variously decorated and marked "Riddle" in ribbon scroll or oblong cartouche.
Unfortunately, that's all the database tells us. No dates or locations, and Riddle is likely just the name of the lockmaker. I'll look in some of my books when I get a chance, but from what we know and what we see from your photos, I would say you are getting a solidly designed but inexpensive mid-19th century half-stocked rifle. I don't see anything about it that says "Hawken." We would be interested in knowing if the top flat of the barrel has any markings, as Phil suggested. If they are faint, you can sometimes make them more readable by rubbing the area with chalk. The rifle is pretty generic, and it would be hard to say for sure where it was made. Maybe somewhere in the midwest or possibly Philadelphia, which was a very important gunmaking center, but late-era halfstocks like that one were made all over the place.
Please don't take offense at any of this. I think it's a plain, simple old rifle, of a type that would have seen a lot of use back in the day. You can bet a lot of rabbits, squirrels, prairie chickens, and maybe even some deer ended up in the family larder thanks to people shooting rifles like that one. I've been reading a lot recently about the Indian wars of the 1850's and 1860's in the midwest and eastern plains, and very few of the ordinary settlers or citizens had fancy or special-purpose firearms. Shotguns, old military surplus arms, and rifles like yours would have been used for defending the home and family. It might not have the cachet of a Hawken or a Leman, but it looks to be in pretty good shape, and a very good representative of an under-appreciated type of firearm. I believe any of us would be proud to have it. Your rifle may very well be a shooter, too. A lot of us here enjoy shooting original guns, and it does them no harm provided they are loaded properly, handled sensibly, and cleaned thoroughly.
By all means, check back in when you get the rifle in your hands, and congratulations on your purchase!
Notchy Bob