Table of contents

Bon Tempe Reservoir

Greg Ehrensing Memorial Volunteer Event

Date: Dec. 4 - 5, 2021
Location: Fairfax, CA
Event Director: - 415.456.8118
Course Setter: Dennis Wildfogel
Type: C; Two days, with limited participation, as in the past; same three advanced-level courses both days; NO BEGINNER COURSE; PRE-REGISTRATION REQUIRED

Photo gallery image (click to enlarge)

Course Setter’s Notes

By Dennis Wildfogel

Covid-19 Considerations

We will be following the Marin County health ordinance guidelines during the event. That generally means that we can hold the event without social distancing and wearing masks. Nevertheless, we should all be cognizant of the ongoing risk of contracting COVID-19, even for those who have been fully vaccinated. Please stay home if you are feeling unwell in any way.

If you are not vaccinated, we ask that you wear a mask while you are in the assembly area, including at the Start and the Finish.

Also, no food will be provided at the assembly area, and water will not be available on the courses. Please bring what you will need.

General Information

The maps are printed at 1:5,000 scale so you can see all the detail. Objects are therefore closer than they might appear. Be sure to read the Map Notes below.

Early on your course, you will be at a control and there will be an out of bounds area directly between you and your next control. Make sure you don't go through the out of bounds area.

The Red course has a map exchange. That is, there are two separate maps, one with the first part of the course and one with the rest of the course. The map exchange takes place at control #16 on this course; this control is on both the first and second maps. Ordinarily, you would drop off the first map at the exchange control, and pick up the map for the second part. But to keep things simple, we will instead use a “map flip”: both maps will be in the map case you receive at the Start, back to back, so that the Part 1 map shows out of one side of the map case and the Part 2 map shows out of the other. Clue sheets for each part are printed on the appropriate map. (The loose clue sheet available at the Registration/Download table has all the controls on it.) On your honor, you should not look at the Part 2 side until you punch control #15, and you should not look at the Part 1 side again after you punch #16. During the #15 to #16 leg, you may look at both sides.

Since we are not permitted to use banners at Bon Tempe, the Finish consists of a control stand with a control flag on it, and a FINISH unit attached to the top. With SI AIR+, you can just wave your E-stick over the FINISH unit to record the end of your run.

The control description “Tree, ruined” refers to a standing, dead tree, represented on the map as a green ×. However, one of those standing dead trees has recently keeled over. It is still being used as a control site for this event, so in the clue sheet the word “fallen” appears under the control description. To help keep things straight, the word “standing” appears under the control description for any other standing dead tree used as a control site.

Careful map reading and full concentration will be rewarded. The terrain is quite benign and also full of detail, which means the challenges will be as much mental as physical. Many of the longer legs have significant route-choice decisions to be made, not just ones where there are two distinct but pretty equal choices, but ones where the first route that catches your eye is not necessarily the one that’s best: cast a broad net and see if you can take advantage of all that the map tells you. On shorter legs, you can be aggressive in going mostly straight, but there are still mini-route choices: look for routes that allow you to move unimpeded, and for routes along which you will have the confidence to move forward with little hesitation. For example, ribbons of clearings are often excellent choices for both those reasons.

There are a lot of controls out there; you may see ones that are not the one you are trying to get to. Don’t just run to a control if you see one​—​it might not be the one you want. Read the map, and the clue sheet!

The course details are on the main event webpage.

Start Procedure

The Start is roughly 50 meters from the Registration/Download table. The START punch unit (on a stand with a flag) will be the only thing at the Start; everything else associated with starting (Start List, clock, CLEAR and CHECK units, maps, and clue sheets) will be at the Registration/Download table.

  1. When you are ready to get a start time, put your name on the Start List at the Registration/Download table, in the appropriate column for your course. Note that starts are only on the even minutes, only one person can start at any given time, and people on the same course must start at least four minutes apart.
  2. One minute before your start time, go to the Registration/Download table, get your loose clue sheet, and punch the CLEAR and CHECK units.
  3. When it's your start time, the event worker there will hand you your map, rolled up. Do not look at your map yet.
  4. Go to the Start (you're not on the clock yet, so you don't have to rush, but don't dally either) and punch the START unit​—​only then can you look at your map. Note that even if you have an SI AIR+ E-stick, you must punch the START unit.


There are several road crossings. Any time you are about to cross a paved road, be alert to the possibility of oncoming cars and bicycles. Bicycles are the bigger danger, especially on downhills, because they often greatly exceed the posted speed limit of 15 mph, and you don’t hear them coming.

It is wet out there. Do not step on fallen logs as they are very slippery. Step over, or go around.

Carry a whistle with you, especially on the Green and Red courses. Those courses spend some time in a remote part of the park where no one ever goes, apart from an occasional orienteer.

Other Items to Note

The warm-up area is the redwood grove south of all the parking lots (not the small grove west of the parking lots). You can also take the fire road immediately east of the redwood grove, up to Lake Lagunitas, and you can run to your heart's content up there.

We are not sending anyone out early to wake up controls. That means if you go out early in the start window, you might come to a control that hasn't been woken up yet. If you have an E-stick that requires you to insert it into the unit, you'll just have to wait an extra second or two. But note that an SI AIR+ E-stick will not wake up a control by waving it over the unit​—​you'll have to actually insert the E-stick into the unit.

Map Notes

All the course maps have been printed at 1:5,000 scale.

Green dots are all small but prominent trees (not bushes). Individual bushes are not mapped. Note: On some other BAOC maps, green dots represent bushes rather than trees. As the green dots on this map are extremely useful for navigation, please keep in mind that they represent small trees, not bushes.

Green ×’s are standing, dead trees, almost always with some limbs still intact. They look like they’ve died of a disease, not from a lightning strike.

Tight green hatching (i.e., vertical stripes) can either be a patch of bushes or a small area of broken limbs. The latter appear to be former green ×’s that have completely deteriorated.

Light green and medium green are used only in forested areas. Patches of bushes in open areas that impede movement are represented by green hatching​—​widely-spaced stripes if it’s not too difficult to get through, tightly-spaced if it is more difficult. Some forested areas are marked with green hatching rather than solid green because visibility is good despite the difficult running.

Brown ×’s are rootstocks. Stumps are not mapped.

All the yellow on the map represents rough open. Unlike many of our other venues, where rough open can be slow running (e.g., tall grass, or sharp thistles, or rough ground from grazing cows), all the rough open at Bon Tempe is pretty-good to good running.

Quite a few rock features have been added to the map. Most of the boulders are between one meter and half a meter high, and most of the mapped stony ground isn’t very extensive. Nevertheless, both of these rock features are very noticeable in the terrain.

The size of the green circles (prominent trees), green ×’s and brown ×’s has been reduced, because they were taking up too much space. Some of the green ×’s are a little hard to see against a background of green stripes. The symbols for boulders and stony ground have not been reduced in size, so those features stand out on the map more than they stand out in the terrain.

The difference between green unfilled circles and green dots: More than anything it’s the width of the trunk and the width of the canopy. Some of the green dots are tall but skinny trees, but in many cases it depends on what else is around. If, say, there are five trees fairly close together in a large meadow, all skinny, but one of them is considerably bigger than the others, then that one is probably mapped with a green circle, even though if it had been in an area with many larger trees it would have been mapped as a green dot.

When a tree is at or near the edge of the forest, it can be difficult to discern whether it is mapped as part of the forest or as a distinct tree. If I found myself looking around trying to figure out which tree was the one mapped as a prominent tree, then I figured it wasn’t sufficiently prominent and changed it to be part of the forest, that is, if its canopy was touching the canopies of one or more other trees. Navigation on the courses for the 2021 event does not depend on you being able to make this distinction.

When two trees are alone together in a meadow and their canopies are just barely touching: Is that a copse (white patch) or two prominent trees? If the canopy looks like one continuous canopy, and there is clearly more than one trunk, then it’s mapped as a white patch. The reverse situation also occurs: There are seemingly-lone trees in meadows that, on closer inspection, actually have two trunks. Sometimes these are mapped as a single prominent tree, sometimes as a small white patch.

This area has several prominent gullies. In some places, the gullies are filled with nasty vegetation, making those places poor choices for crossing the gully. Unfortunately, the orienteering map symbol set doesn’t allow for showing that there is vegetation in a gully. A good rule of thumb on this map is that it’s probably not a great place to cross if there is not a clearing on both sides of the gully.

Stands of redwood trees

Black lines enclosing small areas represent stands of redwood trees. (In at least one case, the line encloses only one side of the redwood grove; the other side is set off by some rock features.) The map snippet at the right shows a section of the map with many such stands. This is part of the infamous Hillside of Death​—​the part of the map where these redwood groves are most numerous.

Open with scattered trees

This map uses the “rough open with scattered trees” symbol in quite a few places (something rarely used on Bay Area maps). It denotes an area where there is nothing particularly prominent, but there are too many little things to map and keep it readable. You will notice these patches in the terrain, and you might notice the symbol on the map, but you might not recognize what you’re looking at. The symbol is a regular array of white dots against a yellow background (the second graphic at the right). The problem is that when there are just a few dots, it is easy to think that those little white dots are mapping specific individual round areas of forest (e.g., the third graphic at the right). It won’t matter much if you don’t quite figure out what is going on, but I thought you should be forewarned. In one place you will see a large patch of this symbol, but overlaid with tight green vertical stripes (e.g., the bottom graphic at the right). However, it’s hard to notice the white dots since they’re covered by the green stripes. What is being represented is a large open field that has become choked with bushes, with an occasional tree sticking up.

Some stairs are mapped on one of the trails. I was not familiar with that symbol, but it should be obvious what it represents when you see it.

Road cuts sometimes create earth banks on one side and/or drop-offs on the other. These are often not mapped, as that would add too much clutter. That shouldn’t cause any confusion.

The lake level is presently much higher than mapped, covering mapped features on the shoreline in some places. The courses for 2021 don't come very close to the lake shore, so this shouldn't affect anyone.

In large open areas, small patches of vegetation are mapped reasonably accurately and can be relied on for navigation. In large forested areas, though, the vegetation is not mapped with sufficient accuracy to be depended upon for navigation; rather, large patches of green (of whatever shade) within forested areas give one a general indication of the (lack of) runnability in that area.