Acorns always come from oak trees, but this oak tree has a single green acorn that is there year 'round. Not sure what it fully means, but it's there. As for the cache, if you use the idea of a 4' X 6' oak beam as a measurement, you will most certainly find this cache.
Sebz gur terra npbea, 4' bire naq 6' hc jvyy or gur pnpur.