In the 1990s, Disney wanted to expand the Disneyland Resort, and add a second gate (second park). They came up with the concept of a Sea Park thay was originally going to open in Long Beach, CA. (This idea then became Tokyo DisneySea, the best Disney Park which opened in 2001).
After the Long Beach failure, another park was proposed:
WESTcot, or a Cali version of Epcot. This was also dropped due to lack of budgeting, and more money was focused on DisneySea.
Then, the Knott family announced they were putting Knott's Berry Farm up for sale, and the idea of converting Knott's into a Disney Park, or "Disney America" was proposed, but shot down due to propsed cost and other issuses.
Finally, California Adventure was born, an elaborately themed park, made as a tribute to the golden state. The park in it's planning stages was a glorious thing; unfortunately, much of that themng was dropped due to cost, and the park opened to terrible reviews in 2001, and had was considered to be the worst darkride on the PLANET.
Despite this however, Disney is making a comeback with this park, adding the Bugs Land in 02', Tower of Terror in 03', ridding themselves of the failed darkride SuperStar Limo, and replacing it with a Monsters Inc. darkride in 04'. Various other changes were made, but the park was still lacking, until 2006, when the ten year reconstruction of California Adventure was first announced, along with the addition of Toy Story Mania.
The plan called for many new areas, and shows.
So far, we have: Silly Symphony Swings (Orange Stinger Re-theme) World of Color, Little Mermaid, Goofy's Sky School (Muhallond Madness Re-theme), new entry gate, and next year: CARSland.
All in all, the park has drastically been improved.
But...What's on the horizon?
In October of 2010, Malibomer, the park's tower ride was removed, to make way for a 2015 darkride.
For years, the Redwood Challenge Area of the park has been lacking another major ride.
What's Next?
Haru, California Adventure, if it had been done at a later date, say 2-3 years later, it would have been so much better. Disney tried building two 200 million+ dollar theme parks at once, very bad idea.