Source: Geophysical Research Letters

The processes that form continental crust from the denser basaltic rocks of the upper mantle may make the lower lithosphere denser than the underlying mantle. One theory holds that the lower lithosphere splits away and sinks into the mantle in a process called foundering. Conclusive evidence of foundering, however, has been hard to come by.

Peering deep under California’s Sierra Nevada, Schulte-Pelkum and Kilb discovered new evidence of lithospheric foundering in progress. The team imaged the lower crust and uppermost mantle beneath the Sierra Nevada with receiver function analysis, which uses seismic waves that change as they cross structures beneath the surface.

They also studied earthquake data from the Advanced National Seismic System Comprehensive Earthquake Catalog, or ComCat. They found a band of seismicity in the central Sierra, in which small earthquakes (ranging from magnitude 1.9 to 3.2) occur at the unusual depths of 40 kilometers and greater.

Differences in receiver functions along the mountain range revealed a distinct layer in the mantle, which grows gradually less distinct farther north. This aligns with the existing hypothesis that a section of the lithosphere beneath the southern Sierra sank (foundered) millions of years ago.

A slab of colder continental lithosphere also has the capacity to crack, rather than to stretch and flow like hot material typically found at such depths. This likely also explains the presence of such deep earthquakes in the central Sierra, according to the authors.

The researchers found no evidence of this layer in the northern Sierra, indicating foundering has yet to progress to that region.

This work aligns with previous studies that found a gradient Moho, rather than a sharply defined crust-mantle boundary, under the Sierra. It also matches previous suggestions that a cold mantle anomaly under the Great Valley region to the west may be dense lithosphere lost to the foundering process. Foundering has been ongoing in the Sierra for at least 3 million years according to this hypothesis, and the researchers say it may be progressing northward. This region provides evidence of a process of differentiation that occurs throughout Earth’s crust, they argue. (Geophysical Research Letters, https://doi.org/10.1029/2024GL111290, 2024)

—Nathaniel Scharping (@nathanielscharp), Science Writer

Citation: Scharping, N. (2025), Deep beneath California’s Sierra Nevada, Earth’s lithosphere may be peeling away, Eos, 106, https://doi.org/10.1029/2025EO250020. Published on 17 January 2025.

Text © 2025. AGU. CC BY-NC-ND 3.0
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COLORADO SPRINGS, Colo. (KKTV) – On Thursday around 4:10 p.m. a crash at southbound N Nevada Avenue and Mount View Lane blocked several lanes of traffic.

The City of Colorado Springs said the left northbound turn lane and right, left and center southbound lanes were closed.

As of 4:27 p.m., there were no updates on when those lanes would reopen.

Copyright 2025 KKTV. All rights reserved.

The Nevada Legislature begins its lawmaking session on Feb. 3, starting a 120-day spirit to get hundreds of bills considered before the Legislature adjourns until 2027.

Nevada is one of four states that meets biennially (the others being Montana, North Dakota and Texas). The state’s 21 senators and 42 assemblymen and assemblywomen have about four months every odd year to introduce bills, update laws, establish the biennial budget and any other legislative work that may come up.

This year, the Legislature will adjourn – called sine die – on Monday, June 2.

Part-time legislatures, also known as citizen legislatures, were more common in state governments in the past, according to David Damore, a UNLV professor of political science. But a “legislative professionalism” movement in the 1960s and 1970s changed that for many other states.

“Over time, consistent with Nevada’s libertarian ethos, there’s been a tug of war between the people and the Legislature through direct democracy,” Damore said.

The Nevada Constitution originally called for regular sessions to be no longer than 60 days. In the early to mid- 20th century, however, sessions went longer but were only officially recorded at 60 days long. In 1958, voters removed that limitation from the Constitution and sessions grew lengthier until 1998. Then, voters approved a constitutional amendment limiting each legislative session to 120 days.

Damore said the part-time legislature plus term limits – also established through a voter-approved constitutional amendment – can make lawmaking more challenging.

“One of the criticisms of that is because of the turnover and lack of staff support, there’s a real reliance on party caucusing for determining how people are going to vote,” he said. “Party-line voting goes up because that’s the cue they take – the only one that’s really available to them.”

It’s possible for lawmakers to work more than four months in a year, though. The governor has the power to call a special session, bringing lawmakers back to Carson City for a specific purpose. In 2023, for instance, Gov. Joe Lombardo called a special session that lasted eight days to establish state funding for a Major League Baseball stadium on the Las Vegas Strip.

A petition of two-thirds of the members of each house can also convene a special session, though that has yet to happen in the state’s history, according to a 2023 report from the Legislative Counsel Bureau.

Contact McKenna Ross at mross@reviewjournal.com. Follow @mckenna_ross_ on X.