Finding Old Highways – A Guide – Part 2

Concrete Paving

Concrete is a very durable material. It has many uses, though for our purposes – roadway surfaces, curbs, and sidewalks. Local roadways, such as concrete city streets, won’t be covered in this post. Bridges will be covered in a later post. This durability allows us to get either a relative date of when a roadway was paved or built to an absolute date when we find a date stamp.

  • Style of Paving
Short section of Roberts Rd that is now a driveway.
Short section of Roberts Rd that is now a driveway.
1920's paving near Osborne St. Note the widening work that was done on the right side. Looking west.
1920’s paving near Osborne St. Note the widening work that was done on the right side. Looking west.

As technology has evolved, so has concrete paving. The first concrete paving along State Highways was 10-12′ wide, usually not reinforced with steel. These roads were paved in one single slab of concrete. Roadways of this style were paved from around 1910 to 1915. After 1915, wider paving was used and was generally reinforced. Wider paving ran from 15′, 18′, and a “full” 20′. These are usually referred to as “Single Slab Paving”.

Sometime around 1923, longitudinal joints were added to the concrete paving. This created a “Twin Slab” roadway. This style persists today, though greatly changed. Early Twin Slab roadways had fewer expansion joints running across the lane. After around 1926, this problem was worked out by adding more frequent joints. By this time, each lane was a “standard” 10′. This standard remained until the late 1940’s when lane width started to widen to 12′.

  • Date Stamps
1948 date stamp on Olympic Blvd.
1948 date stamp on Olympic Blvd.

Contractors, either by requirement or pride, usually stamp the concrete roadway, curb, or sidewalk with a date stamp. These stamps vary in location, size, and information. Date stamps marked either the beginning or end of a days paving. As such, the stamp tended to be located near an expansion joint. A general rule with date stamps is “find one, you can find the rest”. This is mostly about the location. Some stamps are in the middle of a lane, some are to the side of a lane. The orientation also varies with stamps. The information contained in these stamps also varies. Early stamps just have the contractor and the date. Later stamps added the engineering station. Without going into too much detail, at this time, about engineering stations, the “zero” point is at the beginning of a road section or project. With little exception, I have had little success in finding a date stamp on Single Slab roadways. Twin Slab roadways are much better with stamps.

Using date stamps and styles as a guide, you can easily date a roadways construction to within a few years. There are other methods you can use, but these aren’t covered here. Some will be covered in later posts. Stay tuned for more posts. Bridges, Road Signs, and more will be covered over the next few weeks. If you have any questions, please post a comment or send me a message.

Finding Old Highways – A Guide – Part 1

When looking for old highways, there are many clues you can use to help discover where old highways ran. This will serve as a partial guide to finding those clues and figuring out the history of a roadway in California.

State Highways

When you are looking for clues if a roadway you are on is an old State Highway, there are a few things to look out for. Depending on the age and location, look out for Right of Way monuments. In California, these are small concrete blocks with a C on the side of them, facing the roadway. They tend to be at the fence line along roadways, at the same distance as the utility poles, or further out. How much they stick out also varies. Some are just a few inches above the ground where others are about a foot high. Look out for these monuments at the beginning or ending of a curve usually about 50-100′ from the centerline of the roadway (or former centerline).

Old C-Block State Highway Right Of Way marker from 1930.
Old C-Monument State Highway Right Of Way marker from 1930.

Other clues tend to be tougher to spot but can be very subtle in appearance. Roadways that were formerly paved with concrete instead of asphalt are usually cracked in a very specific way if the asphalt is old enough. Expansion joints in the concrete, potholes exposing the old paving, or a defined crack running near the roadway edge usually give this away. Older concrete paving was either 15′, 18′, or 20′ wide. Modern roadways are usually 24′ wide, with two 12′ lanes. Look out for this concrete at curves which appear to have been straightened.

Original alignment of the Ridge Route at Tejon Pass. These lanes were built in 1923 on top of the original 1919 Ridge Route concrete.
Original alignment of the Ridge Route at Tejon Pass. These lanes were built in 1923 on top of the original 1919 Ridge Route concrete.


On some roadways bypassed or abandoned after 1964, old postmile markers can be found. These markers are similar to the ones on current State Highways. On a current roadway with R mileage, look for old alignments in the area. R mileage indicates a realignment that took place after 1964, which is the point of “base mileage” for California State Highways.

This milepost was found near Whitaker Summit on old US 99. US 99 was gone legislatively in 1964 so Route 5 took over the numbering here. That is why it shows the mileage for I-5.
This milepost was found near Whitaker Summit on old US 99. US 99 was gone legislatively in 1964 so Route 5 took over the numbering here. That is why it shows the mileage for I-5.

Abandoned roadways are tougher to spot depending on the area climate. Drier climates tend to preserve older paving better than wetter climates. In some areas, the paving itself was removed after the roadway was bypassed. I have found a few sections of roadway relatively intact, complete with old striping, in Central and Eastern California. When the pavement has disintegrated or obliterated, you can look out for areas where there is less vegetation and distinct roadway grade. Sometimes old drainage culverts and bridges are left behind with nothing but dirt grade leading to them.


More paving, both lanes now visible.
More paving, both lanes now visible.

In any area, make sure to take plenty of photos if you find an old alignment. You never really know when the local jurisdiction will come along and either obliterate or repave the roadway. This is fairly common in Los Angeles County as I have found. The most recent loss has been the June 1933 three lane concrete in Gorman along old US 99 which was repaved in the past couple years. Document what you find as best as you can. Doing so will help to preserve the memory of these forgotten roadways for many years to come.

Image of the Week – 3/15/2015

Interstate 5 under construction at Magic Mountain Parkway in 1964.
Interstate 5 under construction at Magic Mountain Parkway and the Santa Clara River in 1964. Old US 99 is visible on the right side.

Twenty Years Online – A Review

When I first posted this website, in December 1995, I never imagined it would grow to what is has become in 2015. I certainly didn’t imagine it would last this long. While some pages have come and gone, the focus of the site has remained – to provide the best information I can about the subjects that I have studied about Southern California. The initial scope of the site was only the Santa Clarita Valley, a smaller area north of the San Fernando Valley in Los Angeles County. My initial idea was to write about the local geology and history, as at that time, there was no information online about those subjects. The site itself predates most of the Internet sites we all use today. Google, Facebook, WordPress, Twitter, Instapress, and more all came after this site which is something I didn’t quite realize until recently. Yes, I’ve had a web presence since before these sites existed yet didn’t know about it until recently. It just never came up. Mind you, all of those sites are far more popular and making money, but I never posted this site for that. I simply wanted to share my knowledge, something that the Internet does quite well.

In the intervening years, I’ve added many pages and expanded the focus. My highway pages are some of the most popular on the site, with my US 99 and US 6 tours being the only page of its kind and at such length. The US 6 tour covers over 350 miles of highway by itself. I sometimes look back at these pages, updating them as I go, and realize that I have written quite a bit of information. My geology pages are recognized by the USGS and the California Geological Survey, something that only makes me want to work harder on them.

The name and even the domain have also changed since 1995. When this site began, it was basically a “Home Page” with local Santa Clarita information. As a result, it had a rather clunky address “”. This address proved to be a problem at times when it came to newspapers wanting to post the address. Few seemed to be able to manage to interpret the tilde properly. This problem pushed me to buy my own domain in 2001, changing the site name and address to “”, which was named the “Santa Clarita Valley Resources Page”, as the site was still focused there. This would be the domain of the site until its most recent change and combination of the San Diego page in early 2014.

Today, in 2015, the site stands out as a resource for the whole of Southern California. It covers geology, highways, history, kayaking, wineries, railroads, and bicycling. It also has pages of photographs of the City of San Diego, my home since 2005. I am quite proud of the site and look forward to the next 20 years online. It has been quite a journey so far with so much more to add, so much more to teach, so much more to learn.

Thank you, readers, for the encouragement and help that you have all given me these past 20 years.

Your Resource For Highways, Geology, And More Throughout Southern California Since 1995

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