Thursday, January 07, 2010

Snowsheds and bridges

From: "McGuire, Margit"

How many snowsheds were built through the Sierra Nevada Mountains at the time the railroad was built?

How many bridges/trestles were built through the Sierra Nevada Mountains at the time the railroad was built?

Margit E. McGuire, PhD
College of Education
Seattle University

Diagrams courtesy of Kyle Wyatt (see below):

Courtesy of Kyle Wyatt

Courtesy of Kyle Wyatt

Courtesy of Kyle Wyatt


Blogger CPRR Discussion Group said...

From: "Wendell Huffman:

I cannot answer the snowshed part of the question with any precision. There were two areas of snowsheds – in the Sierra between Shady Run and Truckee and in eastern Nevada in the Pequop Mountains. The number of miles of sheds varied continually as sections burned and others were added. And, I do not know that the Pequop sheds were installed "at the time the railroad was built".

Treating trestles and bridges as a single group (since most of these structures contained elements of both), they were located at:

American River (both trestles and bridge) this was the longest structure

Arcade Creek (trestle)

Dry Creek (bridge)

Antelope Creek (bridge)

Newcastle (trestle)

Auburn (trestle)

Lovell's ranch first (trestle)

Lovell's ranch second (trestle)

Clipper Gap (trestle)

Clipper Ravine (trestle)

Deep Gulch (combination trestle and trusses) this was the highest structure

Long Ravine (trestle and bridge)

Secrettown Gap (trestle and trusses)

Butte Canon (initially a trestle, replaced with a bridge)

Lower Cascade (bridge)

Upper Cascade (bridge)

South Fork Yuba River (bridge)

Drivers Creek (bridge)

Donner Creek (sometimes called Coldstream--the oulet of Donner Lake)(bridge)

Prosser Creek (bridge)

Little Truckee (bridge)

1st crossing of Truckee (bridge)

Juniper (or Grey's) Creek (bridge)

Alder Creek (bridge)

2nd crossing of Truckee (bridge)

3rd crossing of Truckee (bridge)

4th crossing of Truckee (bridge)

5th crossing of Truckee (bridge)

1st crossing of Humboldt (bridge)

2nd crossing of Humboldt (bridge)

Mary's Creek (bridge)

Maggies's Creek (bridge)

North fork of Humboldt (bridge)

3rd crossing of Humboldt (bridge)

Bishop's creek (bridge).

Those structures that are designated "bridge" often had short trestle approaches. The true trestles had bents every 15, 16, or 16.5 feet center to center (depending on whichever souce you want to believe), while the two noted as having trusses has sections with 40-foot "straining beam" trusses, making them a combination of trestle and bridge. Generally, the major trestles were replaced by fill or eliminated by line changes by 1877.


1/07/2010 5:00 PM  
Blogger CPRR Discussion Group said...

Also see the list of Bridge Stereoviews.

1/07/2010 5:12 PM  
Blogger CPRR Discussion Group said...

From: "McGuire, Margit"

Thank you for the detailed answer!

1/07/2010 5:27 PM  
Blogger CPRR Discussion Group said...

From: "Wendell Huffman"

What I carefully avoided was telling you how many trestle/bridges were in the Sierra Nevada. Someone else will have to define the boundaries of that range!

1/07/2010 5:56 PM  
Anonymous Anonymous said...

To add to Wendell's comments: The American River bridge was 2 spans, 192 feet each in length, both Howe Truss.
At Dry Creek, it was a Burr Truss, 4 spans, 210 feet long, granite piers
At Antelope Creek, it was one span, 51 feet, 4 inches long, granite pier
At Deep Gulch, Strained Beam Truss, 8 spans @40 feet each, granite piers, total length 320 feet.
At Long Ravine, a Howe Truss, 2 spans @150 feet, one span @128 feet, timber piers, 428 feet total length
At Secrettown Gap, Straining Beam Truss, 78 spans @40 feet each, 280 feet total length, timber piers
At Butte Canon, Howe Truss, 2 spans @126 feet. 1 span @ 84 feet, 1 span @73 feet, 409 feet total lenght, granite piers
Lower Cascade, one spam Howe truss @204 feet, another Howe truss @80 feet, 2 straining beams 40 feet each. Total length 364 feet, granite piers
Upper Cascade, 1 Howe Truss 204 feet long, one straining beam @ 40 feet, total length 244 feet, granite piers
South Yuba 1 span Howe Truss, 84 feet long, granite piers
Drivers Creek, 1 span Straining beam 50 feet long, granite piers
Donner Creek, Howe Truss, 2 @126 feet, 2 @ 85 feet, total length 422 feet, granite piers.
If you need more, I have the Trestles also.
G J Chris Graves, NewCastle, Cal.

1/27/2010 1:09 PM  
Anonymous Anonymous said...

A question for Chris Graves or any one that might know the answer: Was the measurement for the length of the bridges the clear span or the length of the truss? I measured the Wadsworth bridge piers and got 196 feet (about) from stone pad to stone pad. The north side pier has been coated in concrete except for the stone pads on which the bridge sets. the south side is mostly original.

I am wondering because I have blue prints for a 202 foot Howe truss bridge from the Denver and Rio Grande and the measurement was for the length of the truss whereas I think the clear span measurement was used for the Bridgeport California bridge for a clear span of 208 feet and an overall length, portal to portal, of 229 feet according to the HAER survey.

John A. Duffy - Reno Nevada

6/01/2010 12:44 PM  
Blogger CPRR Discussion Group said...


Per the above SP 64-ft pony truss, and Phoenix truss bridges from the 1873 and 1885 catalogs, the "official" dimension appears to be from centerline to centerline of the end pins on the bridge shoes – or alternately the center of the pad on the pier.


6/04/2010 2:20 AM  
Blogger CPRR Discussion Group said...

From: "Wendell Huffman"

I am unwilling to apply the term "Burr" to any bridge or part of bridge on the CPRR other than the bridges at Dry Creek and Antelope Creek. Specifically, I find no occasion where anyone associated with the CPRR used that term in connection with the arches applied to the long Howe trusses.

R.S. Williamson’s report of 25 January 1869 states: "The design of the larger bridges is the Howe truss, strengthened, in the maximum spans (which are 204 feet) with strong timber arches springing from the abutments. The smaller spans of the Howe pattern, down to that of 75 feet, are built without this arch, according to the practice of the original inventor. Bridges below the last-mentioned span, with two exceptions, which are of the 'Burr' truss, are simple trusses."

Samuel S. Montague’s report of 1 July 1869 states: "All trussed bridges of spans over fifty feet are built on the 'Howe plan' ... The lengths of the spans vary from 84 to 204 feet. Spans of 204 feet are strengthened by heavy arches connected to the lower cords by suspension rods. Spans of 50 feet and under are 'straining beam trusses' ..."

The various commissioners' reports refer to the shorter trusses as “the common 'Straining Beam' or 'Palladio Truss'."

Whether the dimensions given in various CPRR engineering reports are clear span or overall length has long puzzled me. Robert S. Williamson (1869) gave a nice table of bridges. His column of lengths is labeled "longest span." Montague also recorded bridge dimensions (1864, 1869, and others), but he is not specifically clear what he meant. However, both Williamson and Montague gave a total length value. Because the sums of the individual spans generally equal the total lengths, I believe they were giving lengths of trusses, not clear spans between abutments. However, they were clearly not consistent. Comparing individual truss lengths at the American River bridge with the overall length suggests that M and W were both describing that structure's trusses by clear spans. (That they were inconsistent at the same point suggests that they were copying each other.) Too, Williamson and Montague both ascribe 73.5 feet to the Juniper (Grey) Creek bridge, while the commissioners call it 76 feet long, suggesting W and M were talking about clear span. Unfortunately, the four 204 foot bridges consisted only of the single span, so there is no unique "total length" value with which to compare.

The various commissioners' reports are inconsistent in what they state: sometimes they say "in clear" sometimes not. However, their values generally agree with what Williamson and Montague gave, which makes me think there were mislabeling. I am certain none of the commissioners measured anything; they merely took the values given to them by the railroad.

Your measurement at Wadsworth is interesting, and it is apparently consistent with interpreting the 204-foot dimensions as overall, not clear span. However, the situation may be confused by the erection of the iron bridge in 1889. Interestingly, I find its length given as 208 feet.


6/04/2010 2:54 PM  
Blogger CPRR Discussion Group said...


Ok, I'll agree to back off. "Burr arch" has a lot of common usage, often applied to non-Burr trusses with arches. But I'll suggest instead a more technical description used by the Historic American Engineering Record as applied to the Bridgeport covered bridge in California. They describe it as a Howe truss bridge with auxiliary wooden arch.


6/04/2010 10:21 PM  
Anonymous Anonymous said...

Kyle, Wendell,

Thank you for your comments. I really appreciate the dialog on this subject.

The book "Southern Pacific Lines common Standard Plans" volume 3, describes the current 1907 bridge on page 46 as being 200 feet. It also states that it was erected in 1912. Anyone know if the current bridge was moved there from somewhere else or is it 1907 because that is when it was manufactured?

I will have to stop back by and measure the current bridge from pin to pin and see what I get.

I posted my current CAD progress over on

-John A. Duffy - Reno, Nevada

6/05/2010 3:45 AM  
Anonymous Anonymous said...

6/06/2010 3:56 PM  
Blogger CPRR Discussion Group said...

From: "Wendell Huffman"

My impression is that the existing Wadsworth bridge dates from 1912. The only inspection book I have covering that bridge gives it 203'7" in the "length" column, and then describes it as 1-200'0" through steel pin Pratt span. The report states that the west abutment was built in 1868, wings raised with stone in 1912 and a concrete backwall built in 1912. The east abutment was built of concrete in 1912, with 1868 stone wingwalls. Those changes leave open the possibility that the bridge length changed some.

The engineering stations on either end of the bridge, on the railroad's track and right-of-way map, are 114+79.3 and 112+74.8. The difference between them is 204'5".

All of this is making me think that the old CPRR bridge was indeed 204' in the truss, not the span. But, since that was two bridges ago, I wouldn't want to go too far out on a limb.

I'd be interested in going out there with you, but couldn't locate you in the Reno phone book. (I left a message with on one J.Duffy's answering machine.) I suggest you leave me a message at the Nevada State Railroad Museum 687-6953.


6/06/2010 3:57 PM  
Blogger CPRR Discussion Group said...


OK. I've spent some interesting time copying various photos of CP bridges, and delving into old books on bridges.

The CP bridges with arches attached appear to be generally classified as improved Howe trusses (as has been noted), appearing in a variant from the most common forms in historical texts I saw. In the Central Pacific Howe truss bridges, the basic truss has top and bottom plates made from 4 timbers each, side by side, with gaps between enough to run 3 rods top to bottom (in typical Howe form).

The arches are 2 timbers high, stacked one over the other, with (metal?) keys let into the timbers to keep them from sliding relative to each other. There are 2 arches per Howe truss panel, one are on the inside and another on the outside (total of 4 arches per bridge – in typical form). Vertical holes are bored through the arches in line with the rods in the Howe truss panels, with rods passing through the holes in the arches, so that in the area where the arches are above the plane of the lower plate, 5 rods in line connect below the lower plate. I haven't found a clear enough photo to show the detail of the connection below the bottom plate of the truss, but I'd imagine it is a cast iron plate that receives all 5 rods.

Contrasting the CP bridges to other examples, I have not found any variants that match the CP design exactly. Most drawings of improved Howe trusses have the rods attached radially from the arch to the lower plate of the Howe truss. In the one example I found with vertical rods through the trusses, they do not line up with the rods in the Howe truss panels. In the case of the Bridgeport bridge (apparently the only surviving Howe truss with attached auxiliary arch in the West), the arches apparently have no rods at all, rather being bolted through between the two arches on each Howe panel in the manner that is like the Burr arch attachment method. In the case of the Milton covered bridge in West Virginia (the only other Howe with an arch covered by the Historic American Engineering Record), the arches have slings over them with rods connected to the slings under the arch.

On the CP bridges, the critical photos to consult are all by Alfred Hart - the following stereo cards:
Hart 225 Bridge over First Crossing Truckee River, 204 feet long
Hart 226 Interior of Bridge over first Crossing of the Truckee River
Hart 279 var 1 Fourth Crossing of the Truckee River. 147 miles from Sacramento

Also helpful are:
Hart 224 First Crossing of the Truckee River
Hart 274 Bridge over Truckee River, Eagle Gap
Hart 278 Bridge Below Verdi, Truckee River
Hart 249 Lower Cascade Bridge Above Cisco
Hart 251 Upper Cascade Bridge Above Cisco
Houseworth 1293 Bridge at the Second Crossing of the Truckee River, Nevada (no arch on this bridge)

Houseworth 1517 First Bridge, Alameda Canon, Central Pacific Railroad (no arch)
Houseworth 1518 Creek View under the first Bridge, Central Pacific Railroad (no arch)
Muybridge 866 Trestle and Crossing of the American River near Sacramento-5145 feet long (no arch)
Muybridge 740 Fifth and last crossing of the Truckee, near Wadsworth (with arch - sided over)


6/07/2010 9:19 AM  

Post a Comment

<< Recent Messages