“Floor Piece #4†is a mathematically precise wood construction and is evidence of Sol LeWitt’s experimentation with volume and sequence. The work is in the collection of the Museum of Contemporary Art San Diego and was a museum purchase dedicated to Sebastian Adler, director of the museum from 1973 to 1983.

What if you took the choice holdings of three internationally renowned museums, put them in a giant jar, shook them up and spilled them out? That is what is happening in this seaside city, although with considerable less happenstance.

The new exhibition “Behold America! Art of the United States from Three San Diego Museums” brings together and mixes up the collections of three museums to trace the history of American art. The fusion of the three major collections has resulted in a far grander exhibition than that afforded by a single institution. As a whole, the exhibition makes a significant contribution to the scholarship of American art.

On view at the San Diego Museum of Art (SDMA), the Timken Museum of Art (TMA) and the Museum of Contemporary Art San Diego (MCASD), “Behold America!” explicates the multifaceted nature of American art since colonial days. As such, the exhibition considers the myriad of Americas and Americans that have emerged over the course of the republic. As a central study of American art, it is further an exploration of this seaside city’s cultural interconnections and their influences on American art.

For purposes of organization, the exhibition is ordered according to three central but fluid themes: Figures, Forms and Frontiers. While there is some overlap among the categories, “Figures” is on view at the SDMA and “Forms” is principally on view at the TMA, both of which are in the 1868 Balboa Park. “Frontiers” is on view at the La Jolla location of the MCASD, a particularly fitting site, as the museum is perched on another frontier, the Pacific Ocean. The exhibition is on view at each of the museums through February 10.

Martin Johnson Heade’s 1888 “The Magnolia Blossom†is from the collection of the Timken Museum of Art. Heade painted 17 paintings and about five oil sketches of the magnolia on velvet, many executed when he lived in St Augustine, Fla.

Three museums and three centuries is no easy task. Directors and curators of each institution began to consider “Behold America!” in 2005. As the exhibition developed, the need for a single project curator emerged, and a 2009 Henry Luce grant enabled the hiring of Amy Galpin as project curator to oversee the show, which comprises 175 works by 144 artists.

The exhibition addresses the ways in which artists have expressed colonialism, environmentalism and racial identity through art. Political events, wars, immigration, westward expansion and imperialism, geography and natural beauty †all are subjects for study. Another aspect of interest is southern California itself. Next-door neighbor to Mexico and part of the Pacific Rim, its culture is a heady mix.

That the lion’s share of each museum’s collection was donated by local collectors or purchased by local supporters says much about the community itself. The collections, as does the exhibition, reflect democracy. The exhibition title is taken from the master of democratic verse, Walt Whitman. Like Whitman’s work, the song of the exposition is a serenade to the multifarious aspects of the United States that form the union. Whitman’s words and allusions recur throughout the exhibition. Many of the artists whose work is on view favored Whitman, and their work has great resonance with his tapestries of America. It is no small coincidence that “Behold America” opened in an election year.

A group of portraits from the Eighteenth Century to the Twenty-First Century comprises the “Figures” sector of the exhibition on view at the San Diego Museum of Art. Like the other sections of the exhibition, it pushes the boundaries of what a portrait is †and what a figure is. The earliest work on view in “Figures” is Joseph Blackburn’s 1761 oil on canvas portrait of Thomas Wentworth. The sitter was an early Portsmouth, N.H., merchant and brother of the last royal governor of New Hampshire; his house in Portsmouth remains as one of the finest examples of Georgian architecture in North America.

Asher Durand’s 1848 “Landscape †Composition: In the Catskills†celebrates nature. Like Walt Whitman’s “Song of the Open Road,†the painting describes the power of America’s natural environment. It was purchased by the San Diego Museum of Art in 1974.

Another early likeness is John Singleton Copley’s 1771 portrait of Margaret Kemble Gage, wife of Thomas Gage, commander of the British army in North America. The sitter, wearing a Turkish caftan popular at the time, was born in New Jersey, which gave rise to persistent rumors that her loyalties were divided. The picture was sent to the Gage family estate in England shortly after it was made and remained there until 1984, when it was purchased for the Timken Museum of Art.

The Pennsylvania Quaker-born Benjamin West went to live in England in 1763 where he painted the 1776 allegorical “Fidelia and Speranza,” which is on view. The picture was inspired by Edmund Spenser’s “The Faerie Queen” and was made during a time when the artist was at work on royal family portraits for which King George III appointed him historical painter to the court.

Robert Henri’s 1922 oil on canvas “Bernardita” depicts one of his favorite subjects, Berna Escudero, a girl of Mexican and Native American heritage. He painted her during one of his sojourns in Santa Fe. It and a portrait of the artist’s wife, Margaret Organ Henri, belong to the San Diego Museum of Art.

The three Eighteenth Century works fall under the heading “Figures.” A less definitive portrait might be Bill Viola’s 1992 “Heaven and Earth,” a video installation that comprises two pillars, one suspended from the ceiling and the other mounted on the floor and each with a cathode ray tube. In one is a portrait of the artist’s mother; in the other a portrait of his newborn child. Grandparent and grandchild who never met are united here.

Albert Bierstadt’s grand 1864 “Cho-looke, the Yosemite Fall†is from the Timken Museum of Art collection and the subject is the Western frontier.

Another work in the Figures category is Ben Shahn’s 1957 tempera on board, “Helix and Crystal.” The abstract work is of a scientist depicted molecular structures †the artist’s allegorical reference to nuclear science.

Nonetheless, each work invites the viewer to consider what a portrait reveals.

“Forms” is the central theme of the work on view at the Timken Museum of Art in Balboa Park. The earliest “Forms” are two still lifes by Raphaelle Peale, his 1816 oil on panel example, “Cutlet and Vegetable,” and the still life with peaches from the same year. Peale, son of the portrait painter Charles Peale, was one of the first American painters to make the still life his primary focus. The still life with cutlet is from the collection of the Timken and the still life with peaches is from the San Diego Museum of Art.

The 1900 highly realistic still life “In the Library” by John F. Peto exhibits elements of trompe l’oeil. His work is often likened to that of his contemporary William Harnett, whose 1883 still life “Merganser” is on view for purposes of comparison. Both pictures display a high degree of technical skill, but grand historic events, literary scenes and portraits were more favored by the academies and critics of the time.

Another “Form” of interest is the 1933 oil on canvas “The Primal Wing” by Modernist Agnes Pelton, the artist born in Germany to American parents and arrived in southern California in the late 1920s. Pelton’s work was included in the 1913 Armory Show and was the subject of a number of California exhibitions.

Eastman Johnson maintained a studio on Nantucket for two decades and painted scenes of everyday life. His 1880 “The Cranberry Harvest, Island of Nantucket†is in the collection of the Timken Museum of Art and is on view in the “Frontiers†section of the exhibit, perhaps for the island landscape rather than the figures that populate the scene.

Thomas Hart Benton’s 1940 “After Many Days,” an autumnal tempera and oil on canvas board, is a composition of death †with dying leaves and a skull

Philip Guston arrived in Los Angeles from Montreal in 1919 as a 6-year-old. He was among the artists influenced by the Mexican murals they saw on visits across the border. His late work, the 1977 “Bottles,” evinces Guston’s return to representational art after a long career as an Abstract Expressionist.

Boston artist Sarah Sze created “Drawn” specifically for the La Jolla site of the Museum of Contemporary Art San Diego. A freethinker’s blend of architectural sculpture and drawing, it is made with found objects culled from almost anywhere. While it represents “Frontiers” of making art, it is categorized under “Forms.”

“Frontiers” is on view at the Museum of Contemporary Art San Diego at La Jolla and includes grand landscapes from artists like Albert Bierstadt to contemporary work and installations. “Frontiers” refers to Manifest Destiny and the westward expansion it engendered, as well as to the frontiers of art that artists have explored over the centuries.

“Frontiers” also encompasses the immigrant experience in the United States and all that it portends.

Ellsworth Kelly’s 1963 oil on canvas “Red Blue Green†is illustrative of his experiments with these particular colors. It is part of the collection of the Museum of Contemporary Art San Diego and is on view with other works in the “Forms†section at the San Diego Museum of Art.

John Sloan’s 1913‱925 “Italian Procession” depicts the frontier of the immigrant experience in New York City. He spent more than a decade on the picture, painting it and then leaving it alone for some time and then returning to it. Walt Whitman’s poetry of the city and its peoples resonated with the artist.

“Instant House” is a 1980 installation by Vito Acconci, whose talents extend to sculpture, performance and video art. The piece is a large-scale house with the American flag on the exterior and the Soviet flag in the interior with a central swing inside the four walls that when used causes the walls to rise.

An illustrated and informative catalog accompanies the exhibition and is available at each of the museums. The San Diego Museum of Art is at 1450 El Prado in Balbo Park; www.sdmart.org or 619-232-7931. The Timken Museum of Art is at 1500 El Prado, also in Balboa Park; 619-39-5548 or www.timkenmuseum.org . And the Museum of Contemporary Art San Diego, La Jolla site, 700 Prospect Street; 858-454-3541 or www.mcasd.org .