Sierra Nevada Geology Pics September 2002

Inverted Topography and Eocene Stream Gravels

Table Mountain NNE of Fresno, CA and 2 Roadcuts on I-80 W of Donner Pass

Click this image for full-screen Volcanic Cones

The following sequence of images is taken from California State Highway 168..ENE of Fresno..Table Mountain is an example of Inverted Topography. The paleo-San Joaquin River flowed gently out of the low ancestral Sierra Nevada mountain range. Volcanic eruptions along the spline created LAHAR flows which solidified ~12 MY in the lowest part of the topography, the river channel. During the past 12 million years, the country rock eroded on all sides of the harder-to-erode lava topped lahar flow. The 400+ mile long mountain range has been uplifted and surficial deposits have eroded. This has left the erosion-resistant landform we view today--recording the location of the ancestral San Joaquin river.
click on any of the images to open a midsized (approx. 100K) larger version
--click BACK button on browser to return to this page

View from 4,000 ft elevation (looking NW)

Another view from 4,000 ft elevation (looking NW)--the linear mesa-like landform records the paleo-San Joaquin River.

Volcanic cap rock now records the 12 MY old stream channel--which is present day's highest part of the topography.

View from 1,000 ft elevation

Another view from 1,000 ft elevation--note evidence of lower elevation sub-parallel lava flow

View from 800 ft elevation--definite lower elevation sub-parallel lava flow in this meander bend of the paleo-San Joaquin River

View from 600 ft elevation--clear evidence of multiple flows at this lower elevation

Looking at present San Joaquin Valley floor W near Friant Dam--the Big Table Mountain

Inverted Topography almost even with valley floor--Just N of Fresno W of Hwy 40

Just a few isolated hills remain--10 miles E of Madera--nearing HINDGE-LINE of Sierra Nevada Mountain uplift of the last 3.2 MY

Eocene Stream Gravels (the goal of 1849 gold rush and later miners)--exposed in Dutch Flat Roadcut ~32 miles West of Donner Pass

Eocene Stream Gravels--closeup near Dutch Flat on I-80

The following sequence of images is taken from California State Highway 168..ENE of Fresno..Table Mountain is an example of Inverted Topography. The paleo-San Joaquin River flowed gently out of the low ancestral Sierra Nevada mountain range. Volcanic eruptions along the spline created LAHAR flows which solidified ~12 MY in the lowest part of the topography, the river channel. During the past 12 million years, the country rock eroded on all sides of the harder-to-erode lava topped lahar flow. The 400+ mile long mountain range has been uplifted and surficial deposits have eroded. This has left the erosion-resistant landform we view today--recording the location of the ancestral San Joaquin river.
click on any of the images to open a midsized (approx. 100K) larger version --click BACK button on browser to return to this page
View from 4,000 ft elevation (looking NW)	Another view from 4,000 ft elevation (looking NW)--the linear mesa-like landform records the paleo-San Joaquin River.	Volcanic cap rock now records the 12 MY old stream channel--which is present day's highest part of the topography.
View from 1,000 ft elevation	Another view from 1,000 ft elevation--note evidence of lower elevation sub-parallel lava flow	View from 800 ft elevation--definite lower elevation sub-parallel lava flow in this meander bend of the paleo-San Joaquin River
View from 600 ft elevation--clear evidence of multiple flows at this lower elevation	Looking at present San Joaquin Valley floor W near Friant Dam--the Big Table Mountain	Inverted Topography almost even with valley floor--Just N of Fresno W of Hwy 40
Just a few isolated hills remain--10 miles E of Madera--nearing HINDGE-LINE of Sierra Nevada Mountain uplift of the last 3.2 MY	Eocene Stream Gravels (the goal of 1849 gold rush and later miners)--exposed in Dutch Flat Roadcut ~32 miles West of Donner Pass	Eocene Stream Gravels--closeup near Dutch Flat on I-80