I think Gerald Edgar has the best idea: Contact the school (or even check their website, if they are particularly organized) to see what the textbooks are. Perhaps you can even get a hold of the 9th grade Integrated Math syllabus used by the school.
To guess at your question: Probably the books are published by Houghton Mifflin Harcourt; see here. You could get a textbook in advance, or look for previews online, or check to see if there are videos of math teachers going through these HMH texts on YouTube; but I would not do any of this without first contacting the school simply to ask, again, what text do students in [whatever class] use?
(Side-note: This is not an endorsement of the HMH texts, which I have never used.)
You write in a comment that it is:
All part of the "common core" curriculum.
But Common Core is a set of Standards, and different places in the United States have created different curricula to tackle them. For example, there are quite a number of helpful resources (in my opinion) found through the $\text{engage}^\text{ny}$ site on their Common Core Curriculum; see here for links to both the English Language Arts (ELA) and Mathematics materials.
If you have ever read the actual Standards (if not, here they are for Mathematics) then you will see that they are broken down by grade before high school, and topic (or strand) thereafter. And so the New York link has Pre-K, K, and Grades 1-8; but, subsequently: Algebra, Geometry, Algebra II, and Precalculus/Advanced Topics. So, nothing that is specifically designated as integrated.
You may also be interested in the NYC course overviews; see here. Again, this is all New York based although I recognize your question is about California; still, maybe it is of general interest if you have not looked through Common Core before (and maybe contrasting this with what you find in CA could be of interest). As an example of what is covered in NY, below is an excerpt of their curriculum map from A Story of Functions Curriculum Map and Overview 9-12 (p. 4). Click through for a larger image.
Summary: You could review the topics by directly purchasing an HMH Integrated Math 1 textbook; you could review the topics by looking through the Common Core State Standards for Mathematics to see what is being covered; or you could review the topics by going through the free materials available through the $\text{engage}^\text{ny}$ website. If you ask the prospective school about the materials that they use and edit your question with this additional information, then perhaps I, or others, can give a more substantive answer about recommendations for review textbooks and resources.