Note that getting to one of the art pieces requires steep, slippery, possibly wet off-trail hiking. Via the easiest route, there are a couple of particular spots where a slip could cause real injury, so please be careful, and this is not recommended for young kids (via other routes it would probably be worse). Watch out for poison oak; it's there but should be avoidable.
Art exhibit 1:
Go to N 37°30.838, W 122°17.532
There are several art pieces to enjoy in this immediate vicinity (more than that if you peek inside certain classrooms). The particular mural at the specified coordinates has eight numerical digits painted at the lower-left corner.
ABCDEFGH = Those eight digits (the checksum of these eight digits is 30).
Art exhibit 2:
Add 4 to G, add 5 to H, subtract 3 from C, and subtract 2 from D,
then go to N 37°30.6GC, W 122°17.8HD
Near the middle of this art piece is a representation of a tree.
JK = Count the kids to the left of the tree.
LM = Count the kids to the right of the tree.
RSTU = The four-digit number below the tree.
(Checksum of all eight of these digits is 29.)
Art exhibit 3 (it is recommended that you do not attempt this art exhibit when the ground is wet):
Add 1 to E, add 4 to L, add 4 to R, and subtract 4 from S,
then go to N 37°30.LRS, W 122°18.MEK
Near the right-side base of this art piece (not near the top), you will find a four-digit number.
WXYZ = Those four digits.
Final location of the hide:
Add 3 to T, add 1 to U, add 4 to Y, add 1 to Z, and subtract 1 from B,
then go to N 37°3F.YMU, W 122°1B.ZWT
(Checksum of all fifteen digits of final destination is 58.)
Congratulations to W00fel for his epic FTF!