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This may not be the same species as the rest of your collection. The bright coloration on the peridium, lack of obvious rhizomorphs, and what may be venae externae (external veins – hard to tell in photo) could indicate a Tuber species (a true truffle).
Rhizopogons have appressed (bound to the peridium) rhizomorphs (root-like mycelial strands) on the peridium (outer layer). I don’t notice rhizomorphs on this collection except near the base (which could be a columella). It is certainly an interesting specimen. The nearest thing I would suggest is R. rubescens, but only if you can find more rhizomorphs on it. The peridium is relatively thick, and apparently stains reddish when cut or bruised. But R. rubescens is not known with oak, only with Pinus. Unless there was a pine species somewhere nearby, R. rubescens is a long shot.
Really need a dried collection of this for identification. Most of the specimens you have photographed (except the wormy one) are still immature to my eye. If you can return, collect the darkest-colored specimen on the interior, slice into 1/8-inch slabs, dry, and mail to Dr. James Trappe, c/o Forestry Sciences Lab, 3200 Jefferson, Corvallis, OR 97330. Include a stamped, self-addressed post card for Jim to reply to you. Identification is free.
What are the other possibilities? Gymnomyces, Martellia, and the ever-present species novum or species new to science. If the latter, a voucher collection is an absolute must!