Reasons for dramatic differences in pay for adjuncts?
Highest pay is probably very misleading. What's the median? The survey doesn't say, and so isn't really all that helpful..

It's entirely possible that the highest-paid part-time person at Mt. San Antonio is a doctor teaching a health science course or a lawyer teaching a business course which the North Orange County school doesn't offer, and so market forces may have dictated a higher salary to the part-time person who teaches it.

Trying to draw conclusions from the outliers in a data set is very difficult if not impossible and inadvisable at the very least.