If you are coming east on I-70, the route through Mesa and Powderhorn is much shorter but, as the others have mentioned, steeper and more winding. Jumbo CG, a neighbor of Island Lake, also has electrical hookups and water, but I don't remember if it has flush toilets, if that is important to you. And, while only one man's opinion, Jumbo is listed in the book of the same name as one of "Colorado's 100 Best Campgrounds" and Island Lake, while mentioned in the book, isn't in his top 100.
Of course, if it were me heading from California to Grand Mesa, I would approach the campground from the south for another reason. Getting off I-70 at Grand Junction and heading south on US 50 gives you the perfect excuse for detouring to the "town" (I use that term loosely) of Gateway. Then you can spend some time at the Gateway Museum, one of the most interesting auto museums in the nation. It was built near his ranch by the founder of the Discovery Channel and contains some pretty special cars. But that's just advice from a lifelong "car nut," so you can take it or leave it!