On past?

This is a part of a song.

She lifts her skirt up to her knees,
walks through the garden rows with her bare feet, laughing.
I never learned to count my blessings,
I choose instead to dwell in my disasters.
I walk on down the hill,
through grass, grown tall and brown
and still its hard somehow to let go of my pain.
On past the busted back of that old and rusted Cadillac
that sinks into this field, collecting rain.
Will I always feel this way?
So empty, so estranged.

I don't understand why it says 'on past'.

I know 'on the past' or just when it means 'walk by' without 'on'.

What does 'on past' mean?