bayareawalker's Identifications

Two large mature sleepy rattlesnakes curled up, basking in the sun, in a drainage area. They were not at all bothered by us watching them 3 feet away. Link to 2nd one nearby: https://www.inaturalist.org/observations/214450559

Rattlesnakes are important members of the natural community. They will not attack, but if disturbed or cornered, they will defend themselves. Reasonable watchfulness should be sufficient to avoid snakebite. Give them distance and respect.

Northern Pacific Rattlesnake (Crotalus oreganus ssp. oreganus) is a venomous snake in the Vipers (Viperidae) family. A bite from this snake can cause death or serious illness or injury in humans that may require immediate medical care. It is commonly called a "poisonous" snake to indicate that its bite is dangerous, but that is not correct. It should be called a "venomous" snake. A poisonous snake can harm you if you eat it. A venomous snake can harm you if it bites you.
"Adults are 15 - 36 inches long, (38 - 91 cm) sometimes up to 48 inches (121 cm) with 60 inches being the longest (151 cm). Neonates are about 10.5 inches in length (27 cm). It is a heavy-bodied pit viper, with a thin neck, a large triangular head, and a rattle on the end of the tail consisting of loose interlocking hollow segments. Pupils are elliptical. Scales are keeled. Age cannot be determined by number of rattles on tail.
Rattlesnakes are "pit vipers" which means they have two pits that are used to sense heat when hunting warm-blooded prey - with one pit on each side of the front of the head above the mouth. The ground color is variable, matching the environment - olive-green, gray, brown, golden, reddish brown, yellowish, or tan. Dark brown or black blotched markings, usually with dark edges and light borders, mark the back, with corresponding blotches on the sides. Dorsal blotches mark the front 2/3 of the body, change to dark bars on the body and dark and light rings on the tail which are well-defined and of uniform width. The underside is pale, sometimes weakly mottled. It usually has a light stripe extending diagonally from behind the eye to
Young are born with a bright yellow tail with no rattle - just a single button which does not make a sound. They grow rattles and lose the yellow color as they age. The pattern is brighter on juveniles than on adults. They are primarily nocturnal and crepuscular during periods of excessive daytime heat, but also active during daylight when the temperature is more moderate. They are not active during cooler periods in Winter. In colder areas, they are known to den in burrows, caves, and rock crevices, sometimes in large numbers, and sometimes with other snake species. Rattlesnakes have long, hollow, movable fangs connected to venom glands. The fangs are replaced if broken. A snakes uses its fangs to inject a toxic venom which quickly immobilize its prey. A rattlesnake adult can control the amount of venom injected. Bites that inject venom into humans are potentially dangerous. Sometimes a rattlesnake bites but does not inject venom. These are called "dry bites." A dry bite may still require medical attention. Even a dead snake can bite and inject venom if the jaws open and close reflexively when they are touched."

Guide to the Amphibians and Reptiles of California http://www.californiaherps.com/snakes/pages/c.o.oreganus.html

Link to my favorite Northern Pacific Rattlesnake obs: https://www.inaturalist.org/observations/90924915

Gopher Snake vs Rattlesnake: 5 Key Differences: https://a-z-animals.com/blog/gopher-snake-vs-rattlesnake/

"Rattlesnakes are commonly called a "poisonous" snake to indicate that its bite is dangerous, but that is not correct. It should be called a "venomous" snake. A poisonous snake can harm you if you eat it. A venomous snake can harm you if it bites you. . .
Rattlesnakes are important members of the natural community. They will not attack, but if disturbed or cornered, they will defend themselves. Reasonable watchfulness should be sufficient to avoid snakebite. Give them distance and respect . . .
"Rattlesnakes are also among the most reasonable forms of dangerous wildlife: their first line of defense is to remain motionless; if you surprise them or cut off their retreat, they offer an audio warning; if you get too close, they head for cover. Venom is intended for prey so they're reluctant to bite, and 25 to 50 percent of all bites are dry - no venom is injected. . ."
Excerpts from Snakebit: Confessions of a Herpetologist, Leslie Anthony, Greystone Books, 2008.

"Some Rattlesnakes Losing Their Warning Rattle In S. Dakota" https://www.npr.org/templates/story/story.php?storyId=216924322