The cache is not at the posted coordinates
After a number of trips up into these hills, I decided I wanted to give people another reason to visit all three peaks, and a reward for having done so.
In horse racing, a trifecta is where you select three horses out of the field to win (1st place), place (2nd place) and show (3rd place). A boxed trifecta is where you select three horses to finish as the top three, in any order. If you wheel the trifecta, you select one of the three horses to finish in a particular spot, with the remaining horses taking the remaining spots in any order.
Except we're using peaks here, not horses, so technically this is a Boxed Wheeled Trifecta, with Allison to place - but I decided to shorten the name.
Peak 1 - Monument Peak, elevation 2,594 : At N 37 29.080 W 121 51.945 there is a triangular concrete slab with raised squares holding bolts which have been sheared off.
A = How many of these raised squares.
B = How many bolts in a single square.
Peak 2 - Allison Peak, elevation 2,658 : At N 37 29.986 W 121 52.113 you can see the tallest structure on the Allison Peak antenna farm, which is on the peak and which you cannot climb to. This tallest structure has multiple antennas at the top.
C = Number of antennas at the top of that tallest structure.
D = Last digit of the EBRPD ORD # on the nearby sign.
(C should be the same as the other digit on the sign)
Peak 3 - Mission Peak, elevation 2,517 : At N 37 30.765 W 121 52.885 there is a sighting post that shows you various bay area landmarks. At one time the landmarks are numbered. On the S side of the post there are still two square number tags. Add together the two-digit numbers on these two tags to get EF.
G = E + E + F
Now, a little obfuscation...
H = D - G
I = A + E
J = A + F
The physical cache is located at : N 37 30.CHI W 121 52.FBJ
A few notes:
It's a 10-12 mile hike, with about a 2,000 foot climb.
I brought a half-gallon of water and still ran out. There is water available at N 37 30.707 W 121 52.631.
Carbs get a bad rap. Bring some.
Unless you are absolutely sure it won't rain, pack one of those flimsy emergency ponchos. The weather up there is not necessarily the same as it is down below.
If your car is in the Ed Levin parking lot after dusk, they will send a park ranger to look for you. This does not happen at the Stanford trailhead. I advise leaving a car at the Stanford Trailhead (near Assume Nothing #2) and having someone drop you off in Ed Levin park (near Second Hand Rose) The trailhead is just past the dog park.
It is possible to descend Mission Peak on the Horse Heaven trail. You will go downhill, across a stream, up a small rise and downhill again. When the trail splits, take the left-hand branch. This trail appears to run uphill for awhile, but it curves around and takes you back to the Stanford trailhead.
The Stanford trailhead and Stanford Ave are named after Leland Stanford, who among other things owned a large horse ranch here. There was initially some thought of locating Stanford University along these hills, but the Farm was chosen instead.
The smart money will pick Monument Peak to win.
Other advice is welcome, I will add it here.