DESCRIPTION:
Sutter Buttes, California

Sutter Buttes
Location: California
Latitude: 39.22 N
Longitude: 121.80 W
Height: 600 meters (2,000 feet: South Butte-2,117, West Butte- 1,685, North Butte-?)
Diameter: 16 Kilometers (10 Miles)
Type: Dome field
Number of eruptions in past 200 years: 0
Previous Eruptions/Eruptive History: Erupted 2.5 - 1.5 million years ago
Remarks: Andesite, dacite, rhyolite

Some researchers (e.g. Christiansen and Lipman, 1972) have suggested that Sutter Buttes and the Sonoma and Clear Lake volcanics, south and southwest of Lassen, are older extensions of subduction-related Cascade volcanism. This seems unlikely. If Sutter Buttes were part of a series of older Cascade stratovolcanoes abandoned due to the northward migration of the south end of Juan de Fuca Plate, the "last Cascade volcano" hypothesis would be tenable. But northward, arc volcanoes are young and active. In fact, why do the Cascades have an abrupt southern termination?

Sutter Buttes is an anomalous volcanic landform rising starkly from the flat plain of the Sacramento Valley. As interpreted by Howel Williams, rising magmas uplifted Cretaceous and Tertiary sediments, which quickly eroded. Explosive eruptions, extending perhaps 0.5 million years, accompanied the emplacement of viscous intrusions and extrusions at the center and periphery of the uplift. These pelean domes, which strongly uparched the intruded beds, are andesitic in the central core of Sutter Buttes, and are surrounded by a halo of dacitic to rhyolitic domes. There is no temporal succession of petrologic types, however. Geochemically, the andesites have much higher than normal values of K, Ba, and Sr.

The coalescing central domes are surrounded by gently dipping andesitic sediments interpreted by Williams as waterlaid volcaniclastics produced by reworking of air-fall material ejected from vents in the center of the Buttes. This interpretation may be correct, but "water-laid volcanic deposits" at many other volcanoes have often been reinterpreted as primary base surge deposits. Sutter Buttes needs re-examination.

It is often suggested that Sutter Buttes constitutes the southernmost Cascade volcano, and the feature does occur along the continental extension of the Mendocino Fracture Zone in a region which might have once covered a subduction zone. However, there are great differences in age and morphology compared to the large and young Cascade stratovolcanoes. Additionally, the lack of continuing volcanism at Sutter Buttes confounds analogues with the conventional Cascade volcanoes.

Sutter Buttes is 90 kilometers north of Sacramento and 45 kilometers west of Marysville, California. The buttes are a privately owned nature preserve; permission is required for visits, but public roads pass close for visual inspection.

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