From California Highways and Public Works magazine, January-February 1964 issue.

Mountain Pass

Another 23 Miles Completed On Interstate 15 in Desert

By CARL B. WOLFRAM, Resident Engineer

A high-standard freeway now traverses the Mescal and Clark Mountain ranges via Mountain Pass in the Mojave Desert and connects with the completed Nevada portion of Interstate 15 at the state border.

At a cost of over $6,000,000, the 23-mile improvement beginning 25 miles east of Baker will relieve the traffic congestion experienced in the past.

Regular cross-country traffic, combined with Los Angeles-Las Vegas trips, resulted in many a frustrated queue of cars moving up the curving grades, impatiently waiting for a chance to pass the slow trucks ahead. These sights are now scenes of the past.

The new four-lane divided freeway follows a straight alignment up a steady incline for five miles, starting at the western end of the project to the vicinity of Clark Mountain Bridge. Here, the separated roadways gradually swing apart to form a wide median area providing room for a "dry" streambed.

With roadways converging again, the freeway approaches Mountain Pass Summit. Here, the motorist begins the 11-mile descent to the Ivanpah Dry Lake bed over 2,000 feet below the summit.

Entering Wheaton Canyon, the roadways again sweep far apart, with Wheaton Wash (located on the bottom of the canyon) forming the median. This portion shows a good design solution for a divided freeway through confined, rugged terrain without destroying scenic values. A magnificent view awaits the motorist as he continues towards Nipton Road Overcrossing. The entire Ivanpah Valley extends below, with the New York Mountain Range forming the background.

The roadways again converge, separated by a 100-foot median, and continue for about 10 miles along a straight alignment toward the eastern end of the project.

The existing highway was resurfaced and widened to form the new freeway at three locations. Furthermore, the new alignment crosses the old highway at several places. Construction, therefore, was scheduled in stages, requiring 12 temporary connections or detours, to facilitate the safe and orderly movement of existing traffic patterns.

Some existing service stations had to be removed to accommodate the wider highway. For the benefit of the traveling public during construction, 30 barrels filled with radiator water were placed at intervals along the entire project. During the hot summer months, these water points served as welcome oases for stranded motorists.

Presently, one tree-planted safety rest area for each roadway provides parking facilities and water for the traveler. The water is supplied from three spring sites at nearby Wheaton Springs and piped under gravity flow to drinking fountains at each of the roadside rest areas. Due to the extreme distance between interchanges and commercial facilities in this area, the roadside rests are used frequently.

[the following pictures are in order from south (west) to north (east)]

The new freeway follows a straight alignment up a steady incline until the roadways gradually swing apart to form a wide median.	Looking west from Bailey Road Overcrossing. The freeway traverses the mountain pass plateau.

West of the Roadside Rest Areas, a portion of Wheaton Canyon with Wheaton Wash, a "dry" streambed, dictated the alignment of widely separated roadways.	Looking north from Nipton Road Overcrossing toward the Nevada state line, a distance of nine miles. The freeway follows the old highway (now the new southbound roadway) with a maximum grade of 5.8 percent. Note old Arrowhead Trail of 1924.

Two structural sections were used for this project. The resurfacing section consisted of a minimum of 0.42-foot asphalt concrete over the existing highway. For the major portion of the freeway, the following structural section was constructed: 0.25-foot asphalt concrete on 0.5-foot cement- treated base and 0.33-foot aggregate base. In areas with low-quality basement material, aggregate subbase was placed in addition. Fifteen material sites throughout the project provided the required material for roadway embankments.

Extensive blasting was required to penetrate massive igneous and metamorphic rock formations in the Wheaton Canyon area. The contractor processed nearly 250,000 tons of aggregate for asphalt concrete from rock obtained from the roadway prisms.

Aggregate for base material was obtained and processed by screening operations at a site near the lower part of Wheaton Wash, where high quality alluvial sand and gravel deposits were found.

The contractor used a self-propelled, track-mounted machine to spread aggregate base and cement-treated base in a very efficient manner. The machine is equipped with strikeoff devices, so arranged as to spread windrowed material to a uniform depth and to the full width of two traffic lanes in one operation. A uniform state of consolidation was obtained by means of oscillating rakers. Oscillating cutting screeds, set to uniformly strike off the material to the full width and to the predetermined thickness, accomplished the final shaping of the spread material.

Embankments across Ivanpah Dry Lake were covered with a six-inch blanket of rock to provide protection against the effect of wave action and possible erosion by saturation. An eight-inch layer of the same material was placed under the structural section to protect against saturation of the base by capillary action. Equalizer pipe culverts were installed at 1,000-foot intervals. These precautions are well founded. The danger of large quantities of runoff water filling the "dry" lake from either side always exists following high-intensity summer thunderstorms.

Water, relatively plentiful through this portion of the Mojave Desert, was supplied by four wells near the west end of the project and was piped for 20 miles. Pumped to reservoirs at the Mountain Pass Summit, the water proceeded from there under gravity flow to a terminal reservoir at Yates Well Overcrossing.

Many existing timber bridges had to be removed. This was accomplished by collapsing the concrete deck and igniting the timber pile bents, which were extensively sprayed with oil. Smoldering all night, these burning structures must have been a sight of disbelief to the unsuspecting motorist. Nine new reinforced concrete slab bridges span various "dry" streambeds located throughout the project. Three welded steel plate girder bridges are part of interchanges at Bailey Road, Nipton Road, and Yates Well Road.

As on other projects in the past, special care was taken to preserve native vegetation within the right-of-way. Any necessary disturbed areas, including material sites visible from the highway and roadway slopes, were seeded with native buckwheat at the end of construction activities.

A wide variety of weather conditions were encountered during the construction period. Temperature variations of over 50 degrees F. in a 24-hour period were recorded during almost any month of a year. Snow above 4,000 feet during the winter seasons did not interfere with construction operations as much as did low temperatures. Severe dust and sandstorms within the Ivanpah Dry Lake bed or high-velocity winds through the Mountain Pass area were a common occurrence. Localized thunderstorms of high intensity and of short duration caught many by surprise and caused moderate damage to not yet completed portions of the freeway. During the summer months of 1962, temperatures approaching 120 degrees F. in the Dry Lake area created some uncomfortable working days for state and contractor's personnel alike. Generally, however, beautiful high desert weather conditions prevailed throughout the 20 months of construction activities.

Remains of long-abandoned mining camps are scattered throughout the area. Near Bailey Road Overcrossing, ruins and foundations of Nantan, a busy mining community in 1890, with weekly Wells Fargo stage coach service, are relics of a bygone era. Gold, silver, lead, and copper were successfully mined in the past. A copper smelter is still standing near the western end of the project. Today, only adobe ruins remain of old Ivanpah, a silver camp during the 1870's.

The largest known rare earth deposits in the world exist near Mountain Pass Summit. Today, the Molybdenum Corporation of America is processing the highly concentrated rare earth ore, the only remaining productive mining activity in the area.

Prior to 1924, an unpaved road known as Arrowhead Trail, which was oil-treated shortly thereafter, generally followed meandering "dry" streambeds through Mountain Pass and Wheaton Canyon. Between 1933 and 1937, a greatly improved two-lane highway was constructed, which served as U.S. Highway 91 and 466 until 1963.

Construction on the new freeway was completed on October 25, 1963. J. B. MacDonald and Carl B. Wolfram were resident engineers for the State.

Looking north near Cima Rd (bridge in the distance), with start of grade beyond it.	Downgrade past Bailey Road, with wash in the center median. Altitude around 4000 ft.

Further north, a view of the New York Mountains in the distance.	Before Nipton Rd. Sign says "Down Grade Watch for Slow Vehicles".

At Nipton Road.	View just north of Nipton Road, altitude around 3000 ft. Bridge in the distance is Yates Well Rd, with the Nevada state line further on. While the state line looks close, it takes a while to get there. Jean, NV can be seen in the upper left corner.

Along Ivanpah Dry Lake.	Looking south from Yates Well Road. Bridge in the distance is Nipton Rd.