I've been reading over the 172 page decision, in PDF file, and have studied a main issue which played a role in previous decisions like those in NY, NJ, WA. That issue is the framing of the question of the constitutional right being asserted.
Choosing the phrasing
Specifically its "the right to marry" vs. "the right to same-sex marriage"
The opponents would want the latter phrase. In the CA case (and generally the others), the argument is that, historically, marriage has been defined as only the union of a man and a woman. This is true in the sense that the U.S. and much of the world (except for a few recent changes) has only recognized hetero-only marriage. Same-sex marriage has never been done, and therefore, according to opponents, there is no "right to same-sex marriage" to be found in the constitution.
One guest on Bill O'Reilly's show seemed to agree, as she stated that the CA judges "created a new right out of whole cloth".
However, supporters of gay marriage (which I privately call "marriage equality", "gay people's freedom to marry" or simply "marriage") would prefer the other phrasing of the right to be analyzed: "the right to marry".
You can see I personally feel similar, judging by my prefered phrases in the above parentheses. Watch my bias, people!!
Courts's choice of phrase:
The CA court agreed with the supporters (plaintiff's) phrase. They explain their reasons on pages 51-54 of the 172 page document (page numbers the same for PDF file or paper version of decision.) These reasons include the fact that a prior case on interracial marriage, Perez v Sharp, did not require that judges find a "right to interracial marriage". (p 51-52 )Also the case of Valerie N Supra, where a developmentally disabled woman asserted her right to reproductive freedom, did not ask whether history has allowed disabled to reproduce, but whether the well-established "constitutional right to reproductive freedom" extends to developmentally disabled women. (p. 52)
So we view the issue in terms of a "right to marry". Surely that is in the constitution. Both opponents and supporters agreed with that (p 51, first sentence).
This is despite the fact that the explict declaration of a "right to marry" is not found in the CA constitution (p. 49, under the subheading "A").
The affirmation of that this "right to marry" exists, implicitly, in the CA constitution is found in prior CA court cases dealing with a wide range of issues beyond the gay-rights context, or even beyond the non-gay cases compared by plaintiff's (plaintiff's relied heavily on the Perez v Sharp case, which found bans on interracial marriage unconstitutional).
The next steps
So I've seen how and why the judges phrased their constitutional question:
"Does the well-established, implied constitutional right to marry extend to same-sex couples?"
But the next step is to decide the "yes or no" answer to that question.
They obviously answered yes, but I have not read their reasoning just yet.
The link to the court decision is here., same as link above