"I strike a long trot" refers to a fast trot of his horse
"I pack these hills the summer through" living in the hills to manage the cattle (see Brokeback Mountain)
"I plank the doors" he has covered the doors of the cabins he stayed in during the summer

Aspens are turnin', I think I'd better
Head on down and find some warmer weather
I strike a long trot to canyon's mouth
Hit the valley gona' head her south
And leave behind this cold high mountain wind

Yodelae hoo hoo hoo

Well I packed these hills the summer through
Under skies the clearest blue
But tears turn sharp I feel snow is comin'
I got my season's pay I plank the doors
No use hanging round here no more
In this mountain wind
Cold high mountain wind

Well ice along the creek bank gives a warning
Roll my bed and head out in the mornin'
My achin' bones give me the clue
Find yourself somethin' else to do
And leave behind this cold high mountain wind

Yodelae hoo hoo hoo

Yodelae hoo hoo hoo

With cold high mountain wind
Just like some worried friend
Tellin' me I better git a movin'
Clouds are rollin' way up high
Through the trees comes a lonesome sigh
Of the mountain wind
Cold high mountain wind

Well aspens are turnin', I think I'd better
Head on down and find some warmer weather
I track a long trot to canyons mouth
Hit the valley gona' head her south
And leave behind this cold high mountain wind

Yodelae hoo hoo hoo