"Another thing suggesting the photo is not from Laguna besides the Laguna USRRC entry list for 1966 is that Laguna Seca doesn't support that much grass on the verge as is present in the photo.

Looking further for clues at racingsportscars.com listings shows that:

Steve Diulo raced his Lotus 19-G at the USRRC Laguna Seca event on May 8, 1966 using #29.  Racingsportscars.com has no listing (yet) for the 1965 Las Vegas GP.

Doug Revson ran his #23 Porsche 906 at the Mt. Tremblant race on 7-10-66 and at the Mid-Ohio USRRC event on 8-28-66.  Prior to the Kent USRRC, he raced his tri-color Lotus 23-Climax at the 5-19-66 Bridgehampton USRRC using #23.  However, racingsportscars.com has no listing for the Kent USRRC, so while it is better than the USRRC website for identifying race car numbers, it is no help here.  However, scanning the 1966 USRRC race entries shown on racingsportscars confirms that other Porsche 906 entrants like Scooter Patrick and others did not use #2.  I can find no other race reference to the Mike Fisher Porsched 906, which remains my guess for the car behind Wester in the photo."

(7-21-09)  From Rick Blackmarr:

"Browsing the great new Don Wester archive stuff you posted, I was intrigued by your caption for the last racing photo of Don in his #60 Porsche 906 trailing a ??? Genie and leading another Porsche 906 (#2).  Since I never saw Don drive his 906 (but did see him in RSK and 904), my hunch was to look at the USRRC archive at "classicscars.com".  Searching the 1966 and 1967 seasons, there was only one event that lists Don Wester among the finishers and DNFs.  That event was Round 6 of the 1966 campaign on July 6th at Kent (USRRC Pacific Raceways).  The top ten finishers are shown as follows:

1.   - Mark Donohue / USA           Lola T70 Mk.2 Chevrolet                                  68   1:35:21,400 

  2.   - John Cannon / CDN            McLaren - Chevrolet                                      68 

  3.   - Chuck Parsons / USA          McLaren - Chevrolet                                      67 

  4.   - Bill Eve / USA               Genie - Ford                                             66 

  5.   - Lew Florence                 Lotus 19 Chevrolet                                       65 

  6.   - Don Wester / USA             Porsche 906                                              65 

  7.   - Doug Revson / USA            Porsche 906                                              65 

  8.   - Mike Fisher / CDN            Porsche 906                                              64 

  9.   - Steve Diulo                  Lotus 19 Ford                                            61 

  10.   - Ken Legg                     Lotus 23 Ford                                            60

The #29 car doesn’t have a Genie appearance to me (Bill Eve finished 4th in one).  It looks more like a modified Lotus 19, but Lew Florence used a dark multi-color scheme on his in 1965.  My thinking on the #29 “Genie” is that it is Steve Diulo’s Lotus 19B-Ford (nee Gurney) which was white in the photos I’ve seen from other events, and I think he used #29 in Las Vegas in 1965.  Note the Bardahl (Lotus?) lettering on the door.  I don’t know what livery Doug Revson was running on his 906, but I seem to recall him running it in the 1966 Laguna Can-Am with the stem to stern red-white-blue pattern he used earlier on his Lotus 23.  So my guess is the number 2 Porsche is Mike Fisher’s that placed eighth per the results above."

(8-30-11)   From John Skuja

 I can say without hesitation that is Pacific International Raceway in
Kent Washington..  It was my first chance to see and hear a Carrera 6
perform.  I was just a kid and I remember attending the USRRC race at
Kent.  There were a ton of big bore cars there, including Mark Donahue in
the Penske Lola T70.  But when the green flag fell and all of those big
bore machines were making the ground shake, I could hear Don's C6 howling
it's beautiful sound above all the ground pounding...  I went on to get
trained at the VW factory in 1970 and worked as a Porsche/Audi tech for
the next 40 years.

The car was purchased by Lew Florence and was campaigned for several years
with a painting of two apples on the rear end of the car and "Apple
Knocker" under the graphic, all else was the same.  That car held the
under two liter track record at PIR till they changed the track
configuration, the time was set by Don at 1:25.00 and equaled by Lew, but
never bested..

Don's car is now in the Portland, OR, area, painted red with the same
scallops in the front fenders.  I have attached a picture of the car in
present day livery. The car was restored by Gary Emory, of Porsche Parts
Obsolete in McMinville, OR.  I almost went to work for them, but the
commute would have been too long.  Here is the page from their site about
the car...

(8-30-11)   From John Skuja:

"I can say without hesitation that the venue is Pacific International Raceway in Kent Washington..  It was my first chance to see and hear a Carrera 6 perform.  I was just a kid and I remember attending the USRRC race at Kent.  There were a ton of big bore cars there, including Mark Donahue in the Penske Lola T70.  But when the green flag fell and all of those big bore machines were making the ground shake, I could hear Don's C6 howling it's beautiful sound above all the ground pounding...  I went on to get trained at the VW factory in 1970 and worked as a Porsche/Audi tech for the next 40 years.

The car was purchased by Lew Florence and was campaigned for several years with a painting of two apples on the rear end of the car and "Apple
Knocker" under the graphic, all else was the same.  That car held the
under two liter track record at PIR till they changed the track config- uration, the time was set by Don at 1:25.00 and equaled by Lew, but 
never bested..

Don's car is now in the Portland, OR, area, painted red with the same
scallops in the front fenders.  I have attached a picture of the car in
present day livery. The car was restored by Gary Emory, of Porsche Parts
Obsolete in McMinville, OR.  I almost went to work for them, but the
commute would have been too long.  Here is the page from their site about
the car."