While I like the Gran Fondo idea, I wouldn't limit myself to that completely. If you're going to start your own league from scratch, I'd be open to trying many different things. Have fun, and be creative! There are so many open roads, and forest roads, around this part of the country, you could have long 200km mass-start race/rides, you could have your own ITT, or even TTT, or into the mountains on roads. You get enough people, you can split them into 3-4 groups depending on expected ability. Plan it right, and you could even have a stage race. I can easily see one on Mt. Hood that has
1) ITT up the West Leg Road.
2) Road stage going over the Lolo Pass loop 2-3 times;
3) Road stage going to Lost Lake up the old road, then looping back, and going up to Whatum Lake.
4) Vista Ridge (Road 16) loop.
There's also a slew of paved remote forest roads leading east from Estacada or Ripplebrook towards Timothy Lake and beyond. Plus Larch Mountain early in the year while the gate is still locked. Head down to McKenzie Pass the week it's plowed, but the road is closed (but open to cyclists). Or some of the remote roads south of Mt. Adams even. Then there's all of the roads west and south of Portland.
OBRA and the USCF won't go there because of traffic, insurance, liability, etc. But if your not taking any money, your entire race amounts to friends out riding and having fun.
The most important thing is to get people involved, both to race, or ride, or volunteer to help time, transport, or help with feed zones.
The USCF and OBRA does what they do well, and that's fine, but there's every reason your idea should succeed. Go for it!