Based on album recording and official music video: https://www.youtube.com/watch?v=0eLAB0C_MAM
Standard tuning down a half step:  Eb Ab Db Gb Bb Eb
Using Am chord voicing like in standard, but since it is a half step down it becomes Gm.
Transpose this chart up to Am to see the chord shapes that match Carson's playing.
The Bbmaj chord may be a Bbmaj7(no5)add9 voicing
Notes for Riff
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[Verse 1]
            
Colorado soldi

              
er, put down y

    
our dukes
            
There's nothin

              
g 'round here 

              
but deer and t

             
he breeze to s

hoot
            
You took down 

              
your daddy's l

              
asso to hang t

   
he moon
            
Now you're ski

              
pping on rent 

              
'cause you can

              
't afford the 


room


[Chorus]
            
Polish your bo

          
ots, boy, step

 in time
            
We're heading 

              
out west towar

      
d the county l

ine
             
Gonna bury tha

              
t box of ashes

        
 in the ground
         
I feel a sudde

              
n change comin

   
g around

[Riff/Break]
 

[Verse 2]
            
You should cal

              
l your mama up

 
 sometime
            
Excuses runnin

          
g thin as turp

entine
            
Maybe today it

              
's better just

    
 to roam
            
Cheap sunglass

              
es, Sunday mor

     
ning stoned


[Chorus]
            
Polish your bo

          
ots, boy, step

 in time
            
We're heading 

              
out west towar

      
d the county l

ine
             
Gonna bury tha

              
t box of ashes

        
 in the ground

            
Snakes on the 

          
roadside, vult

ures in the sk

y
            
They lay in wa

         
it for a man t

o die
             
But it ain't t

              
oo late to lea

              
ve this highwa

  
y town
         
I feel a sudde

              
n change comin

     
g around

[Riff/Outro]