NOTHING BEATS a surprise. In Thomas Albright's major survey Art in the San Francisco Bay Area 1945-1980 Gustavo Ramos Rivera rates only a mention in the appendix. Now, a quarter-century later, in two major retrospectives, we can see that Ramos Rivera deserves accolades as one of the leading lights of the second wave of San Francisco's distinctive brand of abstract expressionism.

Ramos Rivera, born in Mexico in 1940, has been splitting his time between the Bay Area and Mexico since 1969. Even if he wasn't trained at the San Francisco Art Institute, where the familiar names of the movement taught, his large canvases often evoke the broad fields of color in Diebenkorn or the adventurous skittering lines that crisscross Frank Lobdell's later paintings.

Ramos Rivera is a protean talent now in his 60s, still working at the height of his powers. His best works combine astonishing bursts of color with endlessly inventive use of collage elements. Thanks to concurrent exhibits, audiences can get a full dose Ramos Rivera's vision. The San Jose Museum of Art focuses on samples of his oil paintings from four decades, while the San Jose Institute of Contemporary Art showcases his prints, drawings and artists' books collaborations.

At the museum, one the earliest canvases, Pausa de la luz/Interlude of Light (1975), features soft, smeary zones of nearly pastel colors running into each other; the approach, which echoes Hans Hoffman, feels somewhat tentative. Better is Noche herida/Wounded Night (1974), in which three passages of very muted red, brown and blue fit into each other like puzzle pieces. At the intersections, flaps of overlapping canvases are sutured together with thread, giving the piece the feel of an improvised shroud. The technique shows up again and again, as Ramos Rivera experiments with collage elements to give his paintings a sculptural texture.

In the 1980s, Ramos Rivera started on a bolder path, asserting himself with free-form color shapes at war with great swashes of black so thick they resemble tar. The magnificent Plegaria/Prayer (1982) commands every inch of its 7-by-4-foot presence. Rising from a dense black surface, rough triangles and squares of color, like semaphores, signal indecipherable messages down the left side.

One section of the painting consists of a square foot or so of chicken wire encrusted with white pigment applied in plasterlike excess. In other spots, Ramos Rivera has painted over chunks of woven wicker. The complex composition is neatly balanced by diagonally opposed rectangles of solid green and yellow.

In Germina cíon/Germination, also from the early '80s, a single exhalation of white brush strokes struggles to be seen in the middle of a inky swirl of agitated black pigment. At times, Rivera's darkness becomes overwhelming, with only a few scribbles of white and ochre dimly visible, as seen in Morada/Home, a 1983 canvas not in the show but which is in the extensive catalog that accompanies the exhibits.

In the 1990s, his palette lightens. Despite its dire title, El circo de la muerte/Circus of Death (1990) sparkles with yellows, greens and reds (as well as a wonderful aqua that will show up later in great abundance) lying easily on top of a slate-gray background, instead of struggling to be released from blackness. Although completely abstract, the painting features what certainly must be a literal pair of crossed batons with flaming tips—the prop of some unseen juggler.

Just in time for the new millennium, Ramos Rivera's paintings turn downright playful, popping with extraordinarily bright colors and simple outlined shapes that start to look like a child's idea of an airplane or a bug. Catedral/Cathedral (2003) sets jauntily distended rectangles and circles of color dancing across a sun-yellow surface. Crawling across the scene is an eight-legged creature from some distant jungle of the imagination.

Ventana del mar/Window to the Sea (2002) sinks into an ocean of pure blue marked with little red boxes and wandering, exploratory lines that sometimes end in exuberant bulbous flourishes.

The splendid Cosas del corazón/Matters of the Heart (2003) looks a bit like a map of San Francisco split between a deep red headed south to the peninsula, with the city proper brushed in orange. The ocean and bay blues surround the image on three sides; white lines like streets divide the painting into fanciful zones.

Ramos Rivera has never limited himself to oils. At the San Jose Institute of Contemporary Art exhibit, his innovative approach to various media is amply displayed. Again, there is a movement from darkness into light. Tatuaje de sombra/Shadow Tattoo and Sin Titulo, from the early '80s, rely on an earthy denseness from which snatches of color seem to emerge, as if being excavated by the artist. In Sin Titulo, the sense of digging is enhanced by the use of a crumbled carton stuck to the surface and dribbled with paint; in another corner, Rivera has painted over a shredded piece of cardboard.

I Could Have Been a Contender (1984) is a collaged cartoon of two boxers cut from a cardboard six-pack holder and glued onto paper. The boxers' ring is sketched in ink and surrounded by tiny pieces of torn paper. To one side, you can see an old-fashioned man in a top hat checking out the action, like a visitor from a Max Ernst collage.

The hand-colored monotype Palo Alto Series No. 26 (2005) revisits the cool blues of Ventana del mar. On this shimmering tropical sea float triangles, tridents and a sketchy outline of a airplane.

The SJICA show also highlights Ramos Rivera's talents as an assemblage artist. Several painted constructions are fashioned from brightly daubed pencils, pens, sticks and small tree branches glued onto trunks and Rube Goldberg armatures that look ready to start moving about the gallery. It is as if the artist, not satisfied with applying every color to every surface he could find, started grabbing his own tools and turned them into sculptures.

Especially impressive is the large Diccionario para ociosos/Dictionary for Daydreamers (1984). This painting/collage consists of two wooden doors attached side by side to create a diptych. These ready-made surfaces are slopped over with color. Three boards nailed horizontally are painted in red, green and white, like the Mexican flag. A swatch of fabric is held together with branches and stuck to the surface with paint. A ziggurat of rough-cut wood scraps extends into space. A jagged broken slat sticks up from the right-hand door, its serrated edge evoking a crown.

Throughout all his works, Ramos Rivera displays an unending fascination with color for color's sake combined with an inventor's guile in using every possible material at hand. Here is an abstract artist who accumulates rather than rarifies.

Gustavo Ramos Rivera Paintings: Eternidades Del Instante, runs through Sept. 10 at the San Jose Museum of Art, 110 S. First St., San Jose (408.294.2787). Rio de Historias/River of Stories, Drawings, Prints and Artists' Books by Gustavo Ramos Rivera runs through May 20 at the San Jose Institute of Contemporary Art, 451 S. First St., San Jose (408.283.8155).

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