1801 California Street, Office high-rise in Denver, United States.

1801 California Street is a 53-floor, 709-foot (216 m) office skyscraper in downtown Denver, completed in 1983. Its brown concrete façade rises in four setbacks, and the plan reads as two interlocked octagonal sections that separate near the roof. An antenna mast brings the total height to 738 feet (225 m). The lobby holds Ink Coffee, 1801 Eatery and the Guard and Grace steakhouse.

1801 California Street was completed in 1983 and became the tallest building in Denver. It held that title for less than a year, as Republic Plaza surpassed it in 1984. US West occupied the offices before Qwest Communications made the tower its world headquarters, and in 2011 the Qwest sign was replaced with CenturyLink's.

Firefighters from the Denver area climb the interior stairs of this building each year to honor those lost on September 11, 2001. The event has become a local way to remember and reflect on that tragedy.

The building is centrally located in downtown Denver with ground-floor dining and cafe options that are accessible during business hours. The surrounding streets are walkable and connect to other downtown shops and attractions.

The structure is made up of two interlocked octagonal sections that separate near the roof, where an antenna sits at the top. This distinctive shape becomes visible from certain angles and helps identify the building in Denver's skyline.