The crosswalks in San Francisco, and many other Bay Area towns, play a 'machine gun' sound when the 'walk' sign is illuminated for pedestrians. A Bay Curious listener recalls hearing chirping sounds in other areas. Why do ours sound the way they do? Plus, we get to know an architect who listens to buildings.

Additional Reading:

An Architect Who Listens To Buildings

Reported by Olivia Allen-Price, Annika Cline and Sam Harnett. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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Listener Britt McEachern is a tour guide in San Francisco, and spends a lot of time walking around city streets. He's noticed grids of glass embedded in the sidewalk and wants to know what they are. Take a journey with reporter Jessica Placzek to learn the purpose and origins of these gems beneath your feet.

Additional Reading:

What Are Those Grids of Glass in the Sidewalk — And Why Are They Purple?

Quiz: Test Your Bay Area Knowledge

Reported by Jessica Placzek. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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This is the second part of our series on Treasure Island.

Listener Gary Pilgrim was taking a drive across the Bay Bridge with his new wife when they decided to stop at Treasure Island. After taking in the sweeping views, he wondered how this manmade island came to be in the first place, and what it's future holds. We're answering Gary's questions in a two-part series exploring the island's past and future. This week: What are the plans for Treasure Island? And does climate change threaten them?

Additional Reading:

Part I: How Treasure Island Got Made — and Why

Part II: Rising Seas and Sinking Land: The Precarious Future of Treasure Island

Reported by Kevin Stark. Edited by Kat Snow. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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Listener Gary Pilgrim was taking a drive across the Bay Bridge with his new wife when they decided to stop at Treasure Island. After taking in the sweeping views, he wondered how this manmade island came to be in the first place, and what it's future holds. We're answering Gary's questions in a two-part series exploring the island's past and future. This week: How was Treasure Island made, and why?

Additional Reading:

How Treasure Island Got Made — and Why

Reported by Kevin Stark. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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Question asker José Muñoz wants to know more about the storied history of this place, which was a pivotal stop-off in Charlie Chaplin's career. Was Niles Hollywood before Hollywood was Hollywood?

Additional Reading:

This Tiny East Bay Town Was Once a Movie Making Hotspot

Reported by Rachael Myrow. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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The Occupation of Alcatraz began on Nov. 20, 1969, when a group of Native American students, calling themselves the Indians of All Tribes, landed on Alcatraz Island. They wanted to return the land to native ownership, and felt they had a right to the land because of the Treaty of Fort Laramie, which said that land deserted by the federal government should be returned to the natives who once occupied it.

Additional Reading:

WATCH: The Occupation of Alcatraz Turns 50, But the Impact of the Movement Lives On

A Look Back at the Occupation of Alcatraz, 50 Years Later

Reported by Alice Woelfle. Produced by Ericka Cruz-Guevarra, Devin Katayama, Kyana Moghadam and Jessica Placzek. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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Kevin Platt was checking out a flag display outside San Francisco's city hall when he noticed the flag from his home state, Texas, was among them. What gives? Plus, we take a quick dive into the history of San Francisco's oldest square — where the announcement of gold was made, and where the state's first public school house once stood.

Reported by Annika Cline and Marisol Medina-Cadena. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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When Bay Curious listener Justin Hartung was growing up in Oakland, he remembers the Bay being blue. After moving to New York for college in the early 90s, and returning back to the East Bay a couple years ago, he noticed a big difference in the hue of the harbor. When did it get so green?

Additional Reading:

Feel Like the S.F. Bay Used to Be Bluer? You're Not Imagining It

Reported by Amanda Font. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Katie McMurran and Rob Speight. Additional support from Julie Caine, Paul Lancour, Kyana Moghadam, Suzie Racho, Ethan Lindsey and Patricia Yollin.

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To celebrate the third birthday of the Bay Curious podcast we are answering listener questions about our favorite episodes, how we make the show, our theme music, the way we choose questions, and questions we wish we received. Also don't miss our birthday celebration on November 14th from 6 p.m. to 8 p.m. at Babe's Monte Carlo in San Francisco. Register at BayCurious.org/events.

Additional reading/listening:

Why Do Some Hate the Nickname ‘Frisco’?

What Would It Take to Make Lake Merritt Swimmable?

Bay Curious has been made possible by Olivia Allen-Price, Jessica Placzek, Vinnee Tong, Ryan Levi, Suzie Racho, Julie Caine, Erika Kelly, Paul Lancour, Kelly O’Mara, Carly Severn, Katie McMurran, Rob Speight, Pat Yollin, Maggie Galloway, Holly Kernan, Ethan Lindsay, and Julia McEvoy.

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San Francisco is 49 square miles, but contains more than 1,000 miles of sewer mains, running under every block. Take a trip with Bay Curious reporter Carly Severn into the depths of the city, and discover an otherworldly cave that has reached legendary status with some urban explorers.

VIDEO: Take A Trip Into San Francisco's Sewer System

Web story: Tunnels Under San Francisco? Inside the Dark, Dangerous World of the Sewers

Reported by Carly Severn. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Suzie Racho and Rob Speight. Additional support from Julie Caine, Paul Lancour, Patricia Yollin, Vinnee Tong and Ethan Lindsey.

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