Turkey. That's only a few years old. That's popular - gets a lot of ProConti teams duking it out. It's not exactly mountainous but includes enough hills to break things up as long as a super dominant train doesn't show up - Greipel won something like 5 stages this year. Even so, despite Columbia's best efforts, Cofidis and ISD insisted on trying to make the race interesting. The website for the race is one of the absolute best in the sport, the presentation was good and the route decent. It has every chance of getting tougher - plenty of mountains in Turkey they can use if they wish. Turkey does not attract a super prestige lineup, but the start list is looking better every year, and the race is becoming more competitive each year.
California would do well to look at that organic growth and think about that. Present the race professionally, use the benefits of the landscape (California has the potential to put together routes befitting most, if not all, of the Old World (legacy of more modern equipment being used when these passes were constructed). Rather than have all the top teams not particularly caring, use the fact that Anglophone cycling is on the up, as teams like Pegasus aim at ProTour and the likes of United Healthcare and Team Type 1 want to go ProContinental. Don't be afraid of having a less star-studded field - a less star-studded field, including many for whom this is the biggest race of the year, will fight harder for the victory than a more star-studded field of people resting after the Spring Classics or building up for another race. And then, when you have a race that people are fighting over legitimately, that's when you can bring in the rest of the ProTour teams. The ones with US interests - Saxo-Sungard, Rabobank, Quick Step, BMC, Radioshack, Columbia, Garmin... they'd show up anyway. You can rely on them bringing at least some marketable names that will allow you to continue to market the race as being one of the elite events. But for God's sake don't pretend it's a Grand Tour... don't talk in the press about how it's on the same level as the Dauphiné and the Tour de Suisse. Talk about building a race with that aspiration, certainly, and emphasise the star riders you can guarantee showing up (the ones on those teams mentioned above) and encourage the home support. Telling us you're delivering a Grand Tour and then delivering what you delivered this year will just mean people in the US don't bother in future, and people outside the US sneer at you. You need to emphasise that it's a long-term project (I know, you don't want to wait) and set expectations accordingly.
Mountain stages are a good idea, but for god's sake don't make it so that it's never-ending climbing at 3-4%. Then you'll drop all of the national pros and the people there on a jolly or out of form, but without providing any of the opportunities for the top pros to attack and gain separation. Also - many of the top pros being invited are the kind who make their gains in a time trial.
With some Colombian teams aiming at ProContinental, they should perhaps be sought. They will bring interest to the mountain stages, and as it will be one of the biggest races they'll have the chance to enter they will likely be really up for the race. Really try to sell the race to ProContinental teams in France, Spain and Italy - having the likes of Bbox there really helped in Canada, for example.