I have a theory - don't know if it is true, that the reason more Ooparts ( out of place artifacts ) are found in the USA is for a couple of reasons. First you have a greater population density, so there is more people per square mile, to stumble on things that are "out there".
The second reason that I think more things are found in the US is that there have been a number of volcanic flows ( thinking B,C,) which have buried things.. Also, in the northern parts, you have permafrost which can keep things locked up tight in the ground.. I do remember a few years back when Chinese coins from I think around the 1500s era were found in the Yukon. Well the powers that be tried to push it under the rug saying that someone some how dropped these ancient coins and they were buried in the permafrost..
If you want an interesting read,, Trying to remember if it was David Thompson or MacKenzie, but I read in their personal journal ( got it from the library ) that during their travels in the northern either Alberta--B.C area they ran into "elephants" ( mammoths ?) and tracks that frightened their Native guides terribly, and if I remember correctly they actually saw the animals.. The Natives were terrified and told them their guns would not stop these animals ..
Why don't the powers that be not bring that journal to the forefront and tell people that "elephants" ( mammoths?) existed not that long ago in Canada..??