The syllable count in your poem isn't right for true haiku, yours is:
6
7
6
By my count.
Good first try tho ๐
To make it right on the syllable count you could just edit it to read...
The warm mountains stand
solid and strong, tall and free
The big bro of hills.
This website is good for checking the syllable count on haiku
https://www.poetrysoup.com/haiku_syllable_counter/
๐
Okay I'll check it out