Welcome to California!
From the places you are suggesting, I assume you will make Southern California as your base, ie flying into Los Angeles? If that is a correct assumption, then the following is a list of suggestions (and I am sure there are other places too) for around that area:
a) Los Angeles (Hollywood, Disneyland, Universal Studios, Santa Monica beaches, etc) - 2 to 3 days depending on how much time you want to spend
b) San Diego (city itself is pretty, SD Zoo, SeaWorld, WildLife park, Legoland)
c) Santa Barbara, Solvang, further out from LA
d) You mentioned Grand Canyon - as has been pointed out, it is in Arizona, but since you are venturing that way, Las Vegas if you like the bright lights. Between Grand Canyon and Zion (plus Bryce Natl), I personally prefer Zion + Bryce vs Grand Canyon, if I had to choose, although, GC is "world famous". And yes, absolutely take the mule ride down to the canyon floor - I hear the GC ones may need reservation up to a year in advance for peak season (Aug might not be) - the one at Bryce is much more manageable, and to me, a lot prettier.
The redwoods you mentioned in the Sequoia Natl are about 4 to 5 hrs drive from LA. I guess you would be renting a car and driving? Keep in mind that Aug can be quite hot in the places you are thinking of going to, and given the drought that Ca is undergoing for the last 4 years, there may be forest fires here and there that could change your plans. But generally, the notices are clear and you would know. Just be prepared but not unduly worried.
Then of course, there is the Northern California, centered around San Francisco. Around SF, you could visit Muir Woods (nearest redwoods, just north of SF), the wine country (1 hr), beaches (cold not for swimming but beautiful rocky beaches), Carmel, Monterey (about 2 hrs), Yosemite,(3-4 hrs), Lake Tahoe (3-4 hrs)...but no disneyland or universal studios.
California, lots to see and do! Welcome!