Timeline

4980 B.C.

 * Rose Quartz, Ruby, Sapphire, and Pearl are "born"/created in Gem Homeworld.
 * Gems arrive on Earth and establish a colony.

Around 3980 B.C.

 * The Kindergarten is used to incubate new gems.
 * Amethyst and other Gems are made.

2980 B.C.

 * Rose Quartz decided to rebel against her homeworld.
 * A battle occurs at the location which would later become the Strawberry Battlefield. Many Gem Warriors fell.
 * Rose's scabbard is lost during battle.
 * Pearl was "a few thousand years old" at the time.
 * Forced Fusion Experiments start.
 * The Pyramid Temple is constructed.
 * The Homeworld Gems leave Earth.

Unknown Time Period

 * The Galaxy Warp goes inactive.
 * The Crystal Temple is constructed.
 * Ruby and Sapphire have decided to stay fused as Garnet.
 * Amethyst was discovered at the Kindergarten and joins the Crystal Gems.
 * Lapis is trapped in the mirror.

1800s

 * "Nearly 200 years ago", Captain William Dewey and his crew are attacked by a gem monster and rescued by the Crystal Gems. Dewey goes on to found Beach City.
 * In the summer of 1862, William Buford Buchanan, Beach City's most notorious arsonist, sets a record 335 fires. He drowns after diving into the ocean trying to evade police.

1900s

 * In 1937, the Beach City Gremlin supposedly caused the Beach City Blimp Explosion.

Recent History

 * Ocean Town is abandoned after an unspecified catastrophe.
 * Greg drops out of community college to become a professional musician and tour the country. He records Space Train to the Cosmos.
 * Roughly two decades before Year 1, Greg falls in love with Rose Quartz and decides to stay in Beach City.
 * Several months later, Greg records a music video with the Crystal Gems, learns about fusion and unsuccessfully attempts to fuse with Rose Quartz.
 * Greg starts growing a beard and records Let Me Drive My Van into Your Heart.
 * Over a decade before Year 1, Rose Quartz records a video for Steven.
 * Over a decade before Year 1, Rose Quartz gives up her physical form and to give birth to Steven Universe.
 * Roughly 5 years before Year 1, the Aqua-Mexican restaurant goes out of business.
 * Roughly 1 year before Year 1, Connie Maheswaran and Steven see each other for the first time at the Boardwalk Parade.
 * A year before the events of Steven and the Stevens, Steven performs naked at Beachapalooza.

Year 1

 * The series starts with the events of "Gem Glow" and "Laser Light Cannon".
 * Dogcopter 3 premieres in February, placing the events of "Lion 2: The Movie" at some point during that month.
 * "An Indirect Kiss" occurs right before the events of "Mirror Gem" and "Ocean Gem".
 * "Ocean Gem" takes place on the first day of summer, placing the events in the first half of Season 1, including Beach-a-Palooza, from "Steven and the Stevens", in spring.
 * "Horror Club" appears to have taken place around Halloween.
 * "Winter Forecast" takes place during winter.
 * "Maximum Capacity" takes place around Beach City's annual New Year's fireworks, marking the end of the year.

Year 2

 * "Marble Madness" takes place in early spring. The first spring buds can be seen on the trees around the Maheswarans' townhouse.
 * "Open Book", "Story for Steven" and "Shirt Club" take place before "The Return" and "Jail Break".
 * "Full Disclosure" takes place right after the events of "Jail Break".
 * Peridot is found during "Keeping it Together", a while after the events of "Full Disclosure".
 * In "Onion Friend", there's a schedule showing when Yellowtail will be home. Based on the crossed out dates on the chart, making it take place at some point in June, before Yellowtail's expected return on the 25th.
 * "Nightmare Hospital" occurs roughly about 1 year after the events of "An Indirect Kiss", in the summer, as mentioned by Connie.
 * "Sadie's Song" occurs 1 year after "Steven and the Stevens", since Beach-a-Palooza is an annual event.

Level 2 Canon

 * Attack the Light takes place at an unspecified point between Fusion Cuisine and The Return, placing it in Year 1 or Year 2.

Non-Canon

 * "Say Uncle" is set before "The Return". Garnet still has her pre-regeneration outfit.