How should I write a "Personal History Statement" - does a lack of "challenges" mean I cannot contribute to diversity?
The previous answer was great, but since it didn't assuage your doubts, I'll try a different approach.

I will rewrite the instructions for you, removing the parts you're having trouble with.


  Describe how your accomplishments led to your decision to pursue the graduate degree for which you are applying. Include any educational opportunities relevant to your academic journey. Your department may have special prompts and directions for the Personal History Statement; be sure to check the requirements.


Sample response: I always felt that my math teacher and I were on the same wavelength.  I always loved going to math class, and my math assignments were always my favorite part of doing homework.  I had a wonderful opportunity in 9th grade when I was invited to participate in _________.  It was an honor to represent my school, and participating in the event, with scores of other math geeks, was thrilling.

You have my permission to stop there.

Now, if you decide to make a stab at addressing the diversity question, consider this: what is the demographic make-up of the state of California, and how did that come to be?  (I will let you find the answer to those questions, as homework.)  Has there been a historical gender imbalance in your field?  Is there anything about you that would make you an effective graduate student instructor, mentor or outreach specialist, enabling you to effectively support the success of underrepresented groups in your field?  Perhaps you have had experience communicating with someone with a different dialect.  Perhaps you had more patience with this than some of your fellow students.  Perhaps you have been lucky enough to be educated in a system where women were not underrepresented in your field, and this experience left you with a firm belief in the role of women in your field. (These are just examples to give you an idea.)