Leaving camp on Day 4, Lynn's 88 stuck briefly in a steep sandy spot, but soon the convoy continued south through the Hot Springs Mountains, which formed the western shore of the ancient lake. On the sandy dirt roads forming this leg of the journey, Lynn and John (as was their custom at least once on every expedition) swapped vehicles. This enabled John to get grounded again in “real” Land Rover driving and attempt once again to master the numerous transmission levers in the 88, while Lynn glided through the rough and dusty bits in air-cushioned, pollen-filtered Range Rover comfort listening to Mozart on the 11-speaker stereo.
 

Fortymile  Desert, West side of Carson Sink Skirting the Hot Springs Mountains Range Rover 4.0 and Series IIA Swap Drivers	Mysterious Pebble Mounds,  10,000 year old Clovis Archaeological Site West Carson Sink

On this leg, we visited an archaeological site where stone tools and weapons have been found dating from the Clovis period 10 to 12,000 years ago – corresponding to the earliest human migrations to North America. In those days, this spot was right on the lakeshore; an ancient beach appears at this level all along the foot of the Hot Springs Range. The arrival of humans coincided with the extinction of the large mammals that formerly lived here -- including woolly mammoths. Among the remains that cannot be explained today are dozens of mysterious pebble mounds – arranged in geometrical patterns. One theory is that the pebbles were removed from the surrounding terrain to improve water runoff, stimulating the growth of useful plants downhill.

Today, the main transcontinental railroad uses the low-lying route along this western edge of the Carson Sink to ease its passage through the mountains of Nevada. We now followed the railroad (and the former southern branch of Lake Lahontan's waters) south past the once-important junction of Hazen, where trains loaded with all manner of supplies once turned off the main line to reach south to the mining boom towns of Tonopah and Goldfield. Following this now virtually unused southern branch of the railroad, we soon negotiated the only significant paved stretch of the route, alongside the Carson River past Lahontan Reservoir. We stopped in the small village of Silver Springs to renew supplies of ice and fuel.
 

Hazen -- a once busy Railroad Junction serving Tonopah & Goldfield. Now even the gas station is closed.	Adrian Valley: Connection between Main and  Walker Sub-Basins of Ancient Lake Lahontan.

At Fort Churchill, we left the river and the pavement again (but not the railroad) to turn south through the Adrian Valley, the only low-altitude connection between the Carson and Walker Rivers. In ice age times, this valley joined the Carson and Walker Lake basins to form one vast uninterrupted body of water. At other times (and as recently as 2,000 years ago), the Adrian Valley channeled the Walker River north into the Carson drainage, completely drying up Walker Lake. Today, the Adrian is dry, but evidence abounds of its past vital role in the Lake Lahontan system. A shelf on the hilllsides approximately 100 feet above the valley floor marks the altitude of the Sehoo Highstand, and light-colored lake deposits visible in the picture above right provide further evidence of the onetime lake.

At its southern end, Adrian Valley connects with the Walker River, the remote north bank of which we now followed eastwards towards Walker Lake. In this remote area called Sunshine Flat we saw evidence of ancient beach barriers some 200 feet higher than the previously assumed peak of Lake Lahontan. Such evidence occurs in several places in the Walker basin, indicating that sometime since the Bishop eruption of 700,000 years ago, Lake Lahontan reached a staggering size – flooding as far south as Rhodes Salt Marsh, and extending from present day Reno to Battle Mountain.
 

Extremely High Shorelines in Sunshine Flat 200 feet above previously assumed maximum	Spectacular Ancient Lake Sediments  alongside the Walker River at Weber Dam

This perspective was a good reminder that since that time (and for 90% of the past 2.5 million years),  the earth has been in an ice age. Roughly every 100,000 years the weather has warmed for a while, but these "interglacials" siuch as we are now experiencing have usually only lasted for 10,000 years or so before cooling off again. We realized once again that we are overdue for another ice age. Reflecting on this sobering prospect, we located and sampled for analysis another layer of volcanic ash that, with luck, might provide further clues to the lake’s uncertain but checkered chronology.

Late in the day, we made camp beside the Weber Reservoir, a dammed up section of the Walker River, designed to provide water for the Walker River Indian Reservation. Some of the largest and most spectacular formations of ancient lake sediments of the entire trip were apparent here.