Coming from either north or south on the Bayshore Freeway (US 101), take the Embarcadero Road exit. Head west on Embarcadero Road (east goes to the baylands). Cross all of Palo Alto, go under the CalTrain tracks, and emerge at the El Camino Real intersection. The Stanford campus starts on the other side of El Camino Real (upper right on map).
After crossing El Camino Real, Embarcadero Road changes name to Galvez Street. Galvez Street splits by the Stanford Stadium: the right lane becomes Arboretum Rd and heads over to the Stanford Shopping Center. The left lane - the one you want - continues towards the central campus.
Galvez soon reaches Campus Drive, which is the main road that forms a ring around the central campus. Just about all other roads heading in from this ring dead end, so you have to use Campus Drive to get anywhere.
Your first problem is to find a place to park. Parking on campus is limited and rules are strictly enforced. From 8 a.m. to 4 p.m., visitors may only park in the visitor lots, where they will be charged $2 per hour, except parking on Lomita Way and Roth Way and the Roth Way Garage, which are closest to the "Oval" in the front of campus, is $2.50 per hour. You can pay with a credit card - note the number of your parking stall and look for the payment kiosk where you can enter it.
After 4 p.m., visitors may park free in any lot, including staff and faculty permit lots, except some student residence lots that are clearly marked for 24 hour enforcement of student only permit parking.
The closest visitor parking to Farrell's office is the lot behind Tressider Student Union (bottom of map). From Galvez Street, at Campus Drive go around the roundabout to head east ("left"). Wind around the campus through athletic and student residence areas. After making a semi-circle around campus, you turn right on Mayfield Ave (four-way stop) and follow it to the Tressider lot.
Other possible visitor parking is on Lomita Drive or Roth Way or its garage near the Cantor Arts Center (Stanford museum). Access these (upper left on map) by turning west (right) on Campus Drive from Galvez Street.
Once parked, plot a walking course to Mitchell Earth Sciences (lower left on map). Farrell's office is in the first level Basement (there is a lower sub-basement level as well), in room B29. This office is immediately adjacent to the south stairs, or just left around the corner from the elevator.