O Brother is The Odyssey set in the south; Blood Meridian is the ur-Western, and isn't based on an epic poem of any sort. (As a nit, I'd also say O Brother is set in the Depression-era South).
I didn't claim Blood Meridian was based on a poem. But I do consider it an odyssey, set in the South (Eastern Texas), and during the Jim Crow era. And last I checked, the Jim Crow era encompassed the 1930s, especially in the South.
By odyssey I mean:
1. a long wandering or voyage usually marked by many changes of fortune
2. an intellectual or spiritual wandering or quest
Blood Meridian is set before Jim Crow, and all across the American Southwest.
It's also just tonally about as far as you could possibly get from O Brother. If it was a comedy, it would be American Psycho. If Fargo was just people being fed into the wood chipper, it would be the comedic counterpoint to Blood Meridian.
