Pacheco Pass

1997 June 6

MarkW, Jim, Jay and I were up at the new Pacheco Pass State Park Friday evening. The spot we used is just a few hundred yards from Hwy 152 in just a little way from the park entrance on the Dinosaur Point road. There is a very large parking lot and a grassy field where we set up. There's room for dozens of scopes and dozens more cars without scopes. It would be a great place for a large party.

The horizons are very good, slighly elevated all around but only very slightly; it's the best of the places we commonly use in that regard. The lights from the highway are not a problem.

As it began to get dark we were excited that it was going to be a very dark site. And indeed it is, by "near town" standards. Blue Canyon or Chew's Ridge it is not. But it is at least as good as Fremont Peak. The light dome from the Bay Area and Gilroy wipes out 1/2 the NW sky and the general light from the central valley shows a little over the hill to the east. But the south was very good, dark right down to the horizon. The diffuse part of the Milky Way that stretches over into Scorpius was clearly visible as was the "Pipe Nebula" within it. Overhead it was almost really dark but only in a fairly small region near the zenith. The elevation is only 1400 ft so the effects of the light pollution are worse.

The real downer is the wind. The temperature was moderate (I would guess in the low 60s or upper 50s) but the constant wind made us all cold. And wiped out the seeing. Mark and Jim were having great success bagging faint galaxies but high-power work was useless. I couldn't even see Jupiter's main two main belts; Mars was a fuzz ball, Antares' companion was invisible.

Oddly, though, the wind is very dependent on one's precise location. The ranger took us over to another spot near the park "headquarters" which was dead calm (but we had already set up). Later we walked 100 yards or so up a tiny dirt road at the edge of our setup spot and again found a place completely sheltered from the wind. But I suspect the seeing may not be that localized :-( The ranger indicated that the wind is less of a problem in the winter.

We had not even a hint of fog. But that was lucky. The ranger said it is often foggy.

Ranger Dooley seems very helpful. I think he really wants us to use the place. There are also two caretaker folks, a married couple who own a C-14. (They've had it for many years and maybe are a little out of it -- they had never seen a Telrad or an LX200 before.) But they were eager to help as well.

Coming home at 2am with no traffic took me only 50 minutes (vs 60 for Fremont Peak).

I think we've found a pretty good spot. For large parties (like the Messier Marathon) we can use the big lots. For little PSC gatherings we can use one of the more sheltered spots. It remains to be seen, however, if the fog and the seeing will cooperate on a regular basis.

-- Bill Arnett

On the evening of Friday, 6 June, 1997, several members of Ptolemy's Supper Club rendezvoused at Pacheco State Park, to investigate its suitability as an observing site. In summary, I think we were pleased...

Pacheco State Park is a relatively new addition to the California State Park system, located south of state highway 152, between Gilroy and Los Banos, just east of the crest of Pacheco Pass. I arrived at about dusk. I glanced at my odometer and clock as I turned off highway 101 at the 152 east exit, in Gilroy, and can report that it was about half an hour, and 26 miles, from that exit to the set-up area. Portions of that stretch of 152 are two-lane road with heavy traffic; you cannot by any means count on driving at 65 miles per hour, and probably shouldn't try to do so -- this route has the just reputation of being dangerous.

State 152 heads straight to the hills northeast of Gilroy, then turns southeast to parallel them for a little, then trends back northeast to enter Pacheco Pass. At the entry to the pass, state 156 from Hollister adjoins 152. The road goes to four lanes about there, and you will be able to get past all the trucks that have been slowing you down. The next major landmark is the well-known "Casa de Fruita" restaurant and shop complex. It has a 24-hour restaurant.

A few miles past Casa de Fruita, 152 starts a serious climb toward the crest of the pass. The turn-off you are looking for is just past the crest, but be advised there is a "false crest" first, followed by a short descent and a climb to the real summit. The exit is to the right, *immediately* past a well-marked truck weighing station and brake-checking area. When you see this area coming up, SLOW DOWN, and if possible, exit into the truck area and drive through it to the side road. One can turn onto the side road, directly from the highway, but there is *NO* *OFF-RAMP*, just an abrupt right turn. If you approach it as if there were the usual freeway exit lane and a place to slow down, you may be in very serious driving trouble.

Half a mile or less down the road is a green gate, to the right, that leads into Pacheco State Park. The area where we set up was a few hundred yards further on, in one of several adjoining parking lots with toilets, a few picnic tables, and space for several dozen cars. There are a number of other areas in the park that are suitable for telescopes, too. I don't know how large these are, but the site can likely handle more equipment than Fremont Peak. What's more, Pacheco State Park is normally day-use only -- it took special arrangements for us to get in. That means, no campers with Coleman lanterns blazing, and no high beams from nocturnal visitors. Let's hear it...

Ranger Dooley met us and collected park fees, which were $5 per car. He advised that because of a special trust fund for this new park, these fees would *not* go into the state general fund, as they do at most places, but would be retained for the specific purpose of operating Pacheco State Park. Later in the evening, volunteer resident attendants Mike and Sandy came by. Mike owns a Celestron 14, and was eager to chat with fellow amateur astronomers.

This location had fairly low horizons in all directions -- I would say less than 10 degrees, often much less. After sunset and dark adaptation, it became obvious that the sky was generally darker than Fremont Peak, particularly from roughly east around through south to southwest. It was not as dark as a Sierra site, or a location with a view over the ocean, but the conditions were notably good for so close to the San Francisco and San Jose metropolitan areas. The light dome of San Jose was the most obvious, with additional glow to the west and southwest from the valley towns along 101. Northeast and east showed illumination from the Great Valley, and perhaps from Livermore. We'd all been to Fremont Peak and to Henry Coe State Park many times, and there is no doubt that Pacheco State Park is as good as or better than either of these locations, as far as sky darkness goes.

We did not get any fog, but there was none in the valley when I was driving home in the small hours of the morning, so that observation is inconclusive. I have no clear sense of whether or not fog would be a problem in this location. There are two ridges between it and the ocean, and the site is slightly on the downwind side of the Diablo Range, which helps. And of course, if valley fog stayed low, it would reduce the sky glow.

We did have an uncomfortable amount of wind. The actual air temperature was balmy, but the breeze made us glad to have warm clothing handy, and was beginning to rattle the Dobsons. However, the wind condition is very local -- there seems to be a jet through Pacheco Pass itself; the site is on the edge of the pass opening, and small changes in location matter a great deal. Furthermore, there is enough rolling terrain to provide wind shadow. Some of us walked about a hundred yards up a road leading away from the site, and found calm air and equally good setup conditions. There are also other parts of the park to investigate.

Seeing was disturbed by the wind, but settled down somewhat in due course. I expect that in a calm part of the park, seeing would be about the same as at Henry Coe State Park.

Telescopes present included 10-inch and 14.5-inch Newtonians, a 12-inch Meade LX200 Schmidt-Cassegrain, and my own 98 mm Brandon refractor. I set up in time to catch omega Centauri at 66x, near the treetops of the low ridge to the south. Later, I finished a Messier survey with the Brandon, poked around in Scorpius and Sagittarius, and spent a while studying the Veil nebula -- both the bright eastern arc and the fine wisps through 52 Cygni were easy at 21x.

The evening included many other highlights. We looked at the fine planetary IC 4406 in Lupus, at 115x in the 10-inch. I had two views of the Bug Nebula, NGC 6302, one in the 10-inch at 115x and one in the 12-inch at 254x -- the latter instrument showed not only the elongation of this planetary but also a few of the wispy tendrils that contribute to its weird appearance. The 12-inch also showed us quasar 3C273, some two billion light-years away, easy at 154x -- a much smaller telescope should reveal it. And the Veil Nebula was also impressive in the 12-inch, at 88x, particularly with an O-III filter -- we could see delicate detail in both the eastern and western portions, as well as in the long, pointy patch that lies about a third of the way from 52 Cygni to the eastern arc.

Pacheco State Park offers excellent prospects as a capacious dark-sky observing site within an easy evening's drive of residents of the San Francisco Bay area. We should by all means go back, and by all means do all we can to develop and maintain good will with the park staff.

-- Jay Reynolds Freeman

Jay is right about the road. It is slow and not much fun. On the two-lane part there are only a few safe places to pass and only two of them are legal. There are always slow trucks and a long string of cars which don't pass making it essentially impossible to get by. Even on the four-lane part cars often creep past the trucks slowing down the whole road in the process. It is almost exactly the same driving time as Fremont Peak but while the last 11 miles up to the Peak are a pleasant change from the usual grind the road to Pacheco Pass is just more of the same. (It's not so bad coming home late at night, though, if you're lucky enough to not get behind a truck on the two lane part.) -- Bill Arnett

Bill Arnett; last updated: 1997 Jun 8