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Bon Tempe Reservoir

Greg Ehrensing Memorial Event

Date: Jan. 21 - 22, 2023
Location: Fairfax, CA
Event Director: - 415.456.8118
Course Setters: Heidi Cusworth (NAV-X), Bill Cusworth (NAV-X)
Type: C; As in the past, limited participation (only for club members) on Saturday or Sunday; PRE-REGISTRATION REQUIRED; NO BEGINNER OR INTERMEDIATE COURSE; same advanced-level courses both days

Please note that time limits apply. Events are typically not canceled due to bad weather.

Event Director’s January 21st Update

It was a great day today at Bon Tempe, and I’m looking forward to another one tomorrow!
If you are coming tomorrow, please note that the parking lot area filled up today a little before 11 AM. This is due no doubt to this being the first weekend of the month with dry weather!
If the parking lot area is full when you arrive, there is a dirt overflow parking area located 200 meters before you reach the main parking area. It is located on the south side of the road, just past the 90-degree road bend as you near the end of the road.
If you have to park there, just walk up the road to the main parking lot, and you’ll see me there.
Scott, Event Director

Course Setter’s January 20th Update

I set out the controls for Bon Tempe today. It was really nice out there, and not as wet as I thought it would be.
I have a few minor updates:
  1. There is a section of Bolinas Road right before the turnoff to the park that is now one-way, because one lane is in danger of washing down the hillside. There is a temporary stop light with an advertised wait of 5 minutes, which seems pretty accurate.
  2. There are some new rootstocks not on the map, some of which appeared due to the recent storms.
  3. There is more vegetation on the map that has been cleared that I didn't have time to map when I was field checking on Jan. 1. I think I fixed everything along the courses, but if you were to stray a bit you might come across some green areas that are now white. The piles of debris will give it away.
Bill Cusworth, Course Setter

January 16th Update

It looks like the weather will give us a break this coming weekend, with the long-term forecast (which I realize can be a tad off) predicting dry conditions each day!
The ground will be soft, but not too muddy, as the terrain is not open range like many of our maps in the East Bay. To avoid the mud, best to stay off the trails as much as possible! Please plan on coming out and having fun in one of the prettiest places to orienteer in the Bay Area.
Due to the limited numbers allowed, the starts for each day will run only from 10 AM until 11:15 AM, with courses closing each day no later than 1:30 PM. No pre-assigned start times, just come to the E-punch table when you are ready, and we will space you out as needed.
I negotiated with the permit person, who agreed we can have up to 40 people each day, so there are still spots open both days if you are thinking of coming. However, you must notify me if you are coming, as we have already printed the maps. If you do not pre-register, you will not be given a map, which ensures that we have enough for everyone who has pre-registered.
Scott Aster, Event Director

Happy Holidays to you all! I hope the end of the year is going well, and you are looking forward to the start of the new year!

The first full weekend of the year begins our 2023 schedule with a visit to our old friend Bon Tempe, land of Redwood circles, rolling, runnable terrain, and of course, the Hillside of Death.

Our permit person at the Water District took vacation and won’t be back until after the first of the year, but she told me verbally that we are good to go. She did not specify the maximum number we will be allowed to have each day, and it might be more than in the past, but I won’t know until next week.

So, I’d like to invite all club members in good standing to notify me if they plan to attend, so I can get a feel for the number of maps we’ll need.

As in the past, this will be our annual, free event, which is planned to have three advanced-level courses: Short (like Brown), Medium (like Green), and Long (like Red/Blue). No beginner or intermediate courses will be offered.

Please contact me via or phone and let me know the day and course you wish to do. You can change your mind before the event, but as I said above, we would like to get an idea of the number of maps to print.

More details will be available next week, when we get our permit and answers to our remaining questions from our permit contact when she returns.

Scott Aster
Event Director
(December 26, 2022)


Starts both days will be between 10:00 and 11:15 AM. People must be ready to start within that period.

The courses will close each day no later than 1:30 PM. Please make sure you are back at the E-punch table by then.


Course Setters’ Notes

By Bill Cusworth

It probably goes without saying that you will get your feet wet on the course, probably within the first few meters on the course. Good luck!


    Course      Length    Climb  Controls
    Brown       3.9 km    175 m     13  
    Green       5.7 km    290 m     19
    Red/Blue    8.3 km    425 m     26

The courses were designed by Heidi & Bill Cusworth. Control descriptions are on the map and loose ones will be provided. There is one standing dead tree used as a control feature​—​its description is shown as Tree, ruined.


The map used in the last several years was made by me in 2015, with some updates by Dennis Wildfogel in 2020-21. I found some new Lidar data that was flown in 2019 that I decided to incorporate into the map. The contours changed a little bit, but probably not too noticeably. I was able to use the Lidar derivative files and newer aerial imagery to place features more precisely, and updated all the vegetation features and trails. Upon field checking, I updated the vegetation for areas that were cleared for fire prevention (early in 2022 according to one of the signs). I also field checked a section of forest just to the NW of the staging area that was off limits in 2015.

I updated the map symbols to ISOM 2017-2, and this will probably be the most noticeable difference. The rootstocks are now brown triangles, a small tree is now a green circle with a white circle in the middle, there is a water tank shown as a blue square. I’ve used a relatively new feature called Open land with scattered trees. This symbol is Rough open yellow with green dots, and is used in areas of scattered tall bushes that had previously been mapped with the Vegetation: slow running, good visibility (undergrowth) symbol (vertical green lines).

Driving Directions

Due to MMWD¹ rules, no BAOC directional signs will be posted. There are several ways to get to Bon Tempe from Highway 101 in Marin.

The approximate coordinates for the event are 37.9497,-122.5974. You can use those coordinates, use Google Maps to get directions to "Lake Lagunitas Parking Lot", or take the route described below.

There are several ways to get to Fairfax from Highway 101 in Marin County. The quickest route is to take the Central San Rafael exit (#452, just north of I-580) and turn west at Third street (a left at the second light if you’re coming from the south, a right at the fourth light if you’re coming from the north). Follow this road for about 3 miles (it changes name three times on the way, eventually becoming Red Hill Ave) until it intersects with Sir Francis Drake Blvd in San Anselmo. Bear right onto Sir Francis Drake Blvd and stay on it until you reach downtown Fairfax.

Turn left at Claus Dr (Rino gas station on the right), and then immediately take another left onto Broadway. Turn right at the next corner (coffee shop on the corner) onto Bolinas Rd.

Stay on Bolinas Rd for 1.5 miles. Turn left onto Sky Oaks Rd​—​that junction is marked by a large, brown, wooden sign on your left with white lettering that says “Lake Lagunitas”, “Alpine Lake”, and “Bon Tempe Lake”. There is also a “Sky Oaks Rd” street sign on the post for the STOP sign for the approaching traffic, but that sign is much harder to see than the large sign mentioning the lakes.

Stay on this road until you reach the ranger kiosk. If the kiosk is not staffed, pay the $8 entrance fee at the pay-and-display machine 150 m further on the right. The automated pay station accepts debit and credit cards, and $1, $5, and $10 bills, but it does not make change.

Proceed on the paved road to the parking lot at the very end, following any signs to Lake Lagunitas. (Note: Do not turn right onto the gravel road to Bon Tempe Dam.) The assembly area is adjacent to the first parking lot you come to in the complex of small parking lots at the end of the road.

¹ MMWD = Marin Municipal Water District