Have you considered the Pomona colleges (they are the same level as UCLA)? They are all located in SoCal! Are you interested in UCLA and SDU due to their paleontology program or do you just like SoCal?
While in the UK uni's admit solely on academics most if not all American colleges look at an application holistically. Here in the US, students have to take every single subject (english, history, math, science) all four years of high school. For areas a student is interested/strong in, he or she can elect to take H/AP course (ie. AP Literature instead of Regular Literature). So I would suggest maybe taking a broader range of subjects if that is possible?
I am a high school senior in Northern California so I can tell you a few things they assess American students by to give you an idea:
- GPA
-Standarized Tests (SAT, ACT, SAT II, AP's)
- Extra-Curriculars * (EC's are HUGE in the American system! If you have a kickass EC it can make up for mediocre grades/test scores)
- 'cool' personal statement (In the UK, I know that there is a very strict format for the personal statement. In the US the more unique and personal your statement is in demonstrating who you are the better!)
Feel free to message me if you have any more questions about American schools or California in general! I have lived here my entire life!