[PaulDavisThe1st]

Water rights were not allocated centuries ago. All water managements systems (more or less) in place when the US took control of the southwest were overridden and replaced by US-style private property rights, a totally different system than exists east of the 100th parallel/the Mississippi. Consequently, they date back at most 1.5 centuries, and in general, less than that.

[oasisbob]

> 100th parallel/the Mississippi.

Small point, but longitudinal lines aren't typically called parallels because they're not parallel to each other.

[dredmorbius]

More specifically: there are parallels of lattitude and meridians of longitude.

https://www.differencebetween.com/difference-between-paralle...

Meridian from "of the noon time, midday":

https://www.etymonline.com/word/meridian

As a mnemonic, the lines of longitude are all equally long (running from pole to pole).