Not too obvious from https://math.berkeley.edu/people/grad . Went through A-C. Found relatively few who put up personal web pages; of those who did, only three named their undergraduate schools: 1 Cambridge, 1 Reed, 1 Michigan.
Math PhD programs do have a reputation of preferring PhD program applicants from schools with what the PhD department considers strong (for pre-PhD students) undergraduate math departments. But that may not align exactly with the usual college rankings that are not math-specific.