[1][2][3] He is most known for site-specific, outdoor sculptures, public art commissions and installations made from repurposed pre- and postconsumer materials, which have been influenced by concepts and processes derived from geology and evolutionary biology.
[4][5] Writers relate his work in formal terms to minimalism, in its materials and emphasis on hands-on processes to postminimalism, and in its unconventional means (natural sites, community involvement, and embrace of ephemerality) to Land art.
"[20][17] In response, he created New Geology #1 (1990), a 15-foot-tall, ten-foot-wide cylinder made of recycled newspapers layered like shales and crowned with earth, grasses and flowers, which New York Times critic Michael Brenson wrote, "sprout[ed] from the ground like an ancient circular tomb.
[15][28][6] Writers distinguish Siegel's work by its combination of traditional sculptural aesthetics (abstraction, centrality of form and composition, craftsmanship) and unconventional means, such as repurposed indigenous materials, scientific concepts and evolving processes derived from nature, and strategies involving organic development, change and risk, and collaboration.
[20] Siegel constructed Squeeze II (1998, Appalachian State University) from old school newspapers and sod, wedging an undulating structure between a grove of hemlocks, the organic curves creating a dialogue with the site's rolling hills.
[8][28] In 2001, he exhibited small wall and tabletop pieces compressing stone, discarded paper, shredded rubber, and tree bark and branches into forms suggesting nests, flora and rock formations.
[28] This work developed into “Wonderful Life” (2002–8), a chronological series of 52 wall pieces made with a limited range of materials that were partly inspired by and titled after Stephen Jay Gould's book of the same name, which reassessed evolutionary theory.
[8][2][39] Critic John Perreault noted a key difference from Siegel's nearly monochromatic newspaper works, describing the series' "garish, contrasting, almost pop colors" as "not necessarily joyous [but] both exuberant and menacing.
He created Collection (2001) for an exhibition of work responding to the Fresh Kills Landfill; The New York Times described its mountain of household rubbish—catalogued by descriptive lists provided by people who donated the items tacked on an opposite wall—as both poetry and an "impressive simulation" of a dumpsite.
(2005, Ingolstadt, Germany), Siegel used 9,000 pounds of donated aluminum Audi body-part rejects to create a giant, slug-like form that jutted from a wall and sprawled across and around a gallery space and its columns.
[7] Biography (2008–13) draws on elements of Siegel's intimate pieces and large installations, combining dense, intricately woven detail, diverse postconsumer materials, and an epic, undulating horizontal sweep.
[2][3][5] Writers have compared it in scale and density to the Abstract expressionist paintings of Jackson Pollock and the Pop assemblages of Nancy Rubins, and visually, to shifting landscape tectonics, a vast topographical map, or DNA.