Here's one of your images.

Was the damaged bark covered with the mulch?

Whatever the answer, that part is permanently damaged. The tree can survive in a reasonable condition if the damage is less than half the circumference. But please don't remove bark to check.

Here is a link that might be useful: base of trunk

Any recommended course of action would be appreciated.

==>>> ignore it.. trees heal themselves ...

if the bark opens itself.. and it will.. as part of the process .... i might carefully start removing it ... but i would NOT go digging in there ...

you did right.. now leave it be

ken

The root flare is still, almost completely buried and if you expose it, healing will vastly accelerate if that's in the cards. In some soils, you can have that much buried, but clearly in your soil, you caint.

Mackel

Is that a Nuttall Oak? That neighborhood looks full of them!

I'm not sure of the type of Oak. The builders planted these along the roadway before the houses were built. It's probably a 5 year old tree.

The damaged area of the trunk spans about 18-24 inches vertically, and maybe the bottom 4-5 inches was covered with mulch until i removed it. And the damaged area is restricted to less than half of the circumference (maybe 120-140 degrees).

When i removed the mulch originally, i removed as much as i could before i started hitting 1/2" diameter roots that had started growing into the mulch pile, so i stopped.

Would spraying any part of it with pruning spray be beneficial? or just continue to leave it alone as Ken suggested above. I did notice some green beetles crawling up and down the damaged area last summer.

i dont think anyone here believes in spraying anything on trees ...

but for one theory of a fungicide type mix.. of which i dont recall ...

my basic premise.. is they cover 50% of the earth.. and do just fine.. until some guy dreams up painting them ... and i call that.. loving them to death .. and voodoo marketing ...

leave them alone.. put down the spray.. and step away ...

ken