I have a collection of HO European engines and cars. I usually picked up a car or engine during travels to Europe. I have several friends who are members of the European Train Enthusiasts (ETE). They run Marklin HO and are very active in the SF Bay Area.
There was a very nice O gauge 2-rail layout exhibited at O Scale West for a few years. The builders had moved to the USA (or perhaps Canada) from England. I have several friends who run European G gauge trains. Again, most of these people immigrated from Europe.
Here are some photos of the O gauge display at O Scale West in 2010.