US Highway 50 Granite Mile Markers: Travelers' Aids Or Roadside Relics?

Jeanine Phillips
American River College
Geography 350: Data Acquisition in GIS
Fall 2006

Abstract

This project examines the relative accuracy of the placement of the historical granite mile markers located on US Highway 50 from Placerville to South Lake Tahoe, California, in September and October of 2006. Location coordinates were recorded with a GPS unit for 32 mile markers while the distance between each marker was measured with a car odometer. GPS data were exported to a GIS and overlayed on a routed highway layer. Distances between each mile marker were determined with the GIS and compared to the distances obtained with the odometer. The data obtained with the GPS/GIS and odometer were not significantly different. The errors in distance between adjacent mile markers were not significant, however, the amount of error from mile marker 1 to each of the other markers was cumulative and tended to increase as distance from mile marker 1 increased. The range of error was 0.2 – 3.5 miles. It is left up to the traveler to decide whether these errors in relative accuracy are important or of no consequence.

Introduction

US Highway 50 on the western side of the Sierra Nevada mountain range was originally surveyed approximately 100 years ago. At that time survey crews placed granite mile markers on the side of the highway to inform travelers of the distance west to the town of Placerville . Today, many of the granite markers still exist on most sections of the highway. New granite mile markers that mimic the original ones also have been placed on new sections of Highway 50 which no longer follow the original routes (marker example: top right photo). However, it is possible and highly probable the granite markers have been moved since their original installation during highway realignments and maintenance, snow removal, land slides and other activities (G. Petershagen, personal communication, 2006).

The goal of this project is to determine if the granite mile markers are reliable distance marks to Placerville. The relative accuracy of the current positions of the markers on Highway 50 and Pony Express Trail between Placerville and South Lake Tahoe will be assessed using GPS/GIS and compared with a car odometer data. The distance from the first mile marker to each of the other markers and the distance between each subsequent marker will be ascertained. In addition, the relative differences in the two data collection techniques will be examined.

FIGURE A. Construction of US Highway 50 in the Sierra Nevada in 1940.

Background

In 1895, the California state legislature designated the Placerville Road as the first state road and renamed it the Lake Tahoe State Wagon Road. It crossed the Sierras from Placerville to the California-Nevada state line. The road remained in disrepair for many years due to lack of state funding, but funds began trickling in from the state in the early part of the 20^th century. During this time the road was surveyed in two phases, the first part of the survey was accomplished in 1900 and the second phase was accomplished in 1907. To mark the survey, surveyors placed granite mile markers which informed travelers of the distance to Placerville. The markers were made by the prisoners at Folsom State Prison. Since at least the gold rush in the late 1850's, it had been a local tradition for roadhouses, resorts, small communities and other businesses along the road to be built at or name themselves according to the distances to Placerville. For example, 3 Mile House, 5 Mile House, 6 Mile House, 14 Mile House, and 29 Mile Ranger Station are a few of the “original” names.

In 1923, the first asphalt was laid on the highway and in 1924, the federal government designated the Wagon Road as US Highway 50, one of the first highway systems to span the continental United States (Figure B). During the 1920's and 1930's highway improvement funds began to trickle in again and old parts of the road were abandoned (Figure A). But it wasn't until 1957 that a portion of the highway in Camino was expanded to 4 lanes.

FIGURE B. Current extent of US Highway 50.

Methods

Data Collection and Processing

The UTM (NAD83) locations of all markers that could be located on Highway 50 and Pony Express Trail while driving a car were recorded as waypoints with a GPS receiver (Garmin GPSMap 76S). Each position was averaged 50-100 seconds. Odometer readings at each mile marker also were recorded. Coordinate and distance data were entered into a spreadsheet, downloaded into ArcMap (ArcView 9.1) and exported to a shapefile. A Caltrans highway layer was downloaded into ArcMap and routed with the Create Routes tool in the Linear Referencing toolset in ArcToolbox. The location of each mile marker on the highway was calculated with the Locate Features Along Routes tool. The distance data were exported to a spreadsheet and converted to miles. Errors in distance from mile marker 1 and each of the other markers were calculated (1-GPS/GIS distance) for Highway 50 markers only. Mile marker 1 was used instead of mile 0 (old Placerville City Hall steps) because the route the original survey crew took from mile 0 to mile 1 was unknown.

Analysis

Data were tested for normal distribution and analyzed by two-tailed t-test or paired t-test to delineate significant differences. Level of significance for both tests were set at P < 0.05. Statistical tests were performed using JMP IN (v4.0.2) software (SAS Institute, Inc.).

Results

Data Collection

Not all mile markers could be located. Markers 1-4, 8, 15-16, 18, 21-27, 30-37, 40-42, 45-49, 51-52 and 56 were located on Highway 50 and markers 9-13 were located on Pony Express Trail (Figure C).

FIGURE C. Map depicting locations of mile markers on US Highway 50 and Pony Express Trail collected with a GPS.

There appeared to be approximately 3 different styles of lettering and symbology on the markers (Figure D), and location did not appear to be a factor in the type of style or condition of the mile marker.

FIGURE D. Photo depicts 3 different styles of mile marker.

All markers were on the south side of Highway 50 or Pony Express Trail, and the majority of markers seemed to be located in areas with wide highway shoulders, although this was not the case on Pony Express Trail. Thus markers may have been placed opportunistically possibly for ease of maintenance or increased visibility to travelers.

Analysis

Data were not normally distributed, but since the data distributions were approximately normal and t-tests are relatively robust to violations of this assumption, the data were analyzed with parametric tests where appropriate. There was a 0.35 percent difference in mean measurements obtained with a GPS/GIS and odometer, but the means were not significantly different (paired t-test, t = -0.2403, P = 0.8116). A graph of the absolute errors in distances between mile marker 1 and each of the other mile markers (Figure E) revealed a lack of independence of each location from the others, i.e., errors in distance were cumulative, thus the data were not tested for significant differences. Absolute errors in distance ranged from 0.2 miles at mile marker 2 to 3.5 miles at mile marker 42.

FIGURE E. The absolute errors in distance between mile marker 1 and each subsequent marker were cumulative in most cases.

The distances between adjacent mile markers were not significantly greater or less than 1 mile on Highway 50 (t-test, t = -0.5992, P = 0.5534, mean = 0.98 miles) (Figure F) nor on Pony Express Trail (t-test, t = -0.7369, P = 0.4667, mean = 0.97 miles) (data not shown).

FIGURE F. Distances between adjacent mile markers. For example, the total distance between markers 18 and 21 is > 1 mile, but has been divided by 3 to find the average distance of 1 mile.

Conclusion

The locations of the granite mile markers on Highway 50 are inaccurate and exhibit location errors of 0.2 – 3.5 miles. Due to the accumulation of errors in distance from marker 1 to each of the other markers and the fact that distances between adjacent markers were not significantly greater or less than 1 mile, it can be assumed that modern day workers who replaced the markers chose placement locations by calculating the distance from the preceding marker and not marker 1 (or mile 0 at the old Placerville City Hall). It's also possible the errors may be due to changes in highway alignment or the abandonment of certain stretches of highway. Route changes could easily shorten or lengthen the highway. If these errors existed during the early days when wagon teams and the first automobiles routinely crossed the Sierra and likely traveled at an average rate of 4 miles per hour, the errors probably would have been more of an issue. However, today's travelers enjoy advanced and more speedy forms of travel relative to those of 100 years ago, so it would be difficult to determine if the inaccuracies of the markers are an inconvenience or annoyance. It will be left up to the individual traveler to decide whether the marker errors in relative accuracy render them roadside relics or whether they can still be considered travelers' aids.

References

Caltrans photographs obtained from http://www.dot.ca.gov/hq/LandArch/scenic_highways/index.htm. Site accessed 12/20/06.

Donaldson RL. 1974. The Placerville Road. Manuscript. San Mateo, California.

Petershagen GF. 1990. Locations of Historic Roadhouses Along US 50. California Department of Transportation. Sacramento, California.