GMAT Sentence Correction (SC) | Re: Seldom more than 40 feet wide and 12 feet deep

Hi Mike,
I am still not convinced why "or" and not "and"
Canal has to be both wide and deep it can't be just one of these!
The question is from OG13/16 Diagnostic test and in the official explanation of why D is wrong here's what is written

""Logical predication; Grammatical construction
The phrase seldom. ..deep is the first half of a modifier that describes theErie Canal. However, because a comma incorrectly follows deep, this phrase appears to be the entire modifier,